LowWEB-HDR-007Information ExposureWeb Apps

Server Software Version Disclosed

Checks whether response headers reveal exact web server, PHP or framework versions.

Why It Matters: Exact versions let attackers match the site against public exploit lists in seconds. Hiding them does not fix vulnerabilities but removes free reconnaissance.
How It Detects: Looks for a version number in the Server header and for the X-Powered-By, X-AspNet-Version and X-Generator headers.
How to Fix: Apache: ServerTokens Prod and ServerSignature Off . nginx: server_tokens off; . PHP: expose_php = Off in php.ini . Remove X-Powered-By in the application or proxy.
How to Verify: curl -sI https://<site>/ | grep -Ei '^(server|x-powered-by)'
CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Control Category: Information Exposure: CIS Controls v8 3, 16; NIST CSF 2.0 PR.DS
Fix Effort: Low
CIS Controls v8 Safeguard: 16.7
NIST CSF 2.0 Subcategory: PR.PS-01
OWASP WSTG v4.2: WSTG-INFO-02
CWE: CWE-497
OWASP Top 10: A05:2021
OWASP ASVS 4.0.3: 14.3.3
NIST SP 800-53 Rev. 5: CM-7, SI-11
References: OWASP HTTP Headers Cheat Sheet
Apache HTTP Server, ServerTokens directive

Learn the theory behind this check: P6 Information Exposure and Misconfiguration, A8 Tracing Findings to Security Requirements.

Source Code

The complete file that defines this check. Run it with openvapt scan --only WEB-HDR-007, or read it offline with openvapt explain WEB-HDR-007.

internal/checks/web/headers.go · Lines 1-303View on GitHub at This Commit

1package web
2
3import (
"context"
"net/http"
"regexp"
"strconv"
"strings"
9
"github.com/openvapt/openvapt/internal/check"
"github.com/openvapt/openvapt/internal/sys"
12)
13
14func init() {
check.Register(&check.Check{
ID:        "WEB-HDR-001",
Title:     "Missing HTTP Strict Transport Security (HSTS)",
Domain:    check.DomainWeb,
Severity:  check.Medium,
CVSS:      "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N",
Summary:   "Checks that HTTPS sites tell browsers to always use HTTPS, for at least six months.",
Rationale: "Without HSTS, the first visit or any typed http:// link can be intercepted and downgraded to plain HTTP (SSL stripping) on public Wi-Fi.",
Detection: "Reads the Strict-Transport-Security header from each HTTPS site's home page, including a redirect response, because browsers honour HSTS on any HTTPS response. Plain HTTP responses are not evaluated. Missing, or max-age below 15552000 seconds (180 days), fails.",
Fix:       "Apache: Header always set Strict-Transport-Security \"max-age=31536000; includeSubDomains\" . nginx: add_header Strict-Transport-Security \"max-age=31536000; includeSubDomains\" always; . Only add 'preload' once every subdomain supports HTTPS.",
Verify:    "curl -sI https://<site>/ | grep -i strict-transport-security",
Refs:      []check.Ref{{Title: "RFC 6797, HTTP Strict Transport Security", URL: "https://www.rfc-editor.org/rfc/rfc6797.html"}, refHTTPHeadersCS, refMDN("Strict-Transport-Security")},
Standards: check.Standards{CWE: []string{"CWE-319", "CWE-523"}, OWASP: []string{"A05:2021"}, ASVS: []string{"14.4.5"}, WSTG: []string{"WSTG-CONF-07"}, NIST: []string{"SC-8"}},
Run: func(ctx context.Context, s sys.System) []check.Result {
	return ForEachSite(ctx, s, func(st Site) check.Result {
		// Browsers honour HSTS on any HTTPS response, redirects
		// included (RFC 6797 section 8.1), so a 3xx is evaluated too.
		if !st.HTTPS {
			return check.SkipR(st.Name, "Site not served over HTTPS (see WEB-TLS-001)")
		}
		h := st.Home.Header.Get("Strict-Transport-Security")
		if h == "" {
			return check.FailR(st.Name, "Strict-Transport-Security header is missing")
		}
		n, ok := hstsMaxAge(h)
		if !ok {
			return check.FailR(st.Name, "HSTS max-age is missing, duplicated or invalid", h)
		}
		if n < 15552000 {
			return check.FailR(st.Name, "HSTS max-age is shorter than 180 days", h)
		}
		return check.PassR(st.Name, "HSTS is set", h)
	})
},
})
50
check.Register(&check.Check{
ID:        "WEB-HDR-002",
Title:     "Missing Content Security Policy",
Domain:    check.DomainWeb,
Severity:  check.Medium,
CVSS:      "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
Summary:   "Checks that each site sends a Content-Security-Policy header.",
Rationale: "A CSP limits where scripts may load from, turning many cross-site scripting (XSS) bugs from account takeover into a blocked request.",
Detection: "Reads Content-Security-Policy from each site's home page. Missing fails. A policy containing 'unsafe-inline' in script-src (without a nonce or hash) or a bare * source is reported as weak.",
Fix:       "Start with a report-only policy to find what the site loads, then enforce, for example: Content-Security-Policy: default-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'self'",
Verify:    "curl -sI https://<site>/ | grep -i content-security-policy",
Refs:      []check.Ref{{Title: "OWASP Content Security Policy Cheat Sheet", URL: "https://cheatsheetseries.owasp.org/cheatsheets/Content_Security_Policy_Cheat_Sheet.html"}, {Title: "W3C Content Security Policy Level 3", URL: "https://www.w3.org/TR/CSP3/"}},
Standards: check.Standards{CWE: []string{"CWE-1021", "CWE-79"}, OWASP: []string{"A03:2021", "A05:2021"}, ASVS: []string{"14.4.3"}, WSTG: []string{"WSTG-CONF-12"}, NIST: []string{"SI-10"}},
Run: func(ctx context.Context, s sys.System) []check.Result {
	return ForEachSite(ctx, s, func(st Site) check.Result {
		if r, skip := st.Redirected(); skip {
			return r
		}
		h := st.Home.Header.Get("Content-Security-Policy")
		if h == "" {
			return check.FailR(st.Name, "Content-Security-Policy header is missing")
		}
		if reason := weakCSP(h); reason != "" {
			return check.FailR(st.Name, reason, h)
		}
		return check.PassR(st.Name, "Content-Security-Policy is set", h)
	})
},
})
80
check.Register(&check.Check{
ID:        "WEB-HDR-003",
Title:     "Site Can Be Framed (Clickjacking)",
Domain:    check.DomainWeb,
Severity:  check.Medium,
CVSS:      "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N",
Summary:   "Checks that each site forbids being embedded in other sites' frames.",
Rationale: "If a page can be framed, an attacker can overlay it invisibly and trick users into clicking buttons (clickjacking), such as 'delete' or 'transfer'.",
Detection: "Passes if the CSP frame-ancestors directive restricts framing (a * or scheme-only source fails), or, without frame-ancestors, X-Frame-Options is DENY or SAMEORIGIN (repeated identical values are accepted; conflicting values fail).",
Fix:       "Send  Content-Security-Policy: frame-ancestors 'self'  (modern) and  X-Frame-Options: SAMEORIGIN  (older browsers).",
Verify:    "curl -sI https://<site>/ | grep -Ei 'x-frame-options|frame-ancestors'",
Refs:      []check.Ref{{Title: "OWASP Clickjacking Defense Cheat Sheet", URL: "https://cheatsheetseries.owasp.org/cheatsheets/Clickjacking_Defense_Cheat_Sheet.html"}, refMDN("X-Frame-Options")},
Standards: check.Standards{CWE: []string{"CWE-1021"}, OWASP: []string{"A04:2021"}, ASVS: []string{"14.4.7"}, WSTG: []string{"WSTG-CLNT-09"}, NIST: []string{"SC-18"}},
Run: func(ctx context.Context, s sys.System) []check.Result {
	return ForEachSite(ctx, s, func(st Site) check.Result {
		if r, skip := st.Redirected(); skip {
			return r
		}
		ok, why := framingRestricted(st.Home.Header)
		if ok {
			return check.PassR(st.Name, "Framing is restricted", why)
		}
		return check.FailR(st.Name, why)
	})
},
})
107
simpleHeader := func(id, title, header, want, summary, rationale, fix string, sev check.Severity, std check.Standards) {
check.Register(&check.Check{
	ID: id, Title: title, Domain: check.DomainWeb, Severity: sev,
	CVSS:      "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N",
	Summary:   summary,
	Rationale: rationale,
	Detection: "Reads the " + header + " header from each site's home page and checks that it is present" + map[bool]string{true: " with the value " + want, false: ""}[want != ""] + ".",
	Fix:       fix,
	Verify:    "curl -sI https://<site>/ | grep -i " + strings.ToLower(header),
	Refs:      []check.Ref{refSecureHeaders, refMDN(header)},
	Standards: std,
	Run: func(ctx context.Context, s sys.System) []check.Result {
		return ForEachSite(ctx, s, func(st Site) check.Result {
			if r, skip := st.Redirected(); skip {
				return r
			}
			v := st.Home.Header.Get(header)
			if v == "" || (want != "" && !strings.EqualFold(strings.TrimSpace(v), want)) {
				return check.FailR(st.Name, header+" is missing or not '"+want+"'", v)
			}
			if header == "Referrer-Policy" && unsafeReferrer(st.Home.Header.Values(header)) {
				return check.FailR(st.Name, "Referrer-Policy unsafe-url sends the full URL to every site", v)
			}
			return check.PassR(st.Name, header+" is set", v)
		})
	},
})
}
simpleHeader("WEB-HDR-004", "Missing X-Content-Type-Options", "X-Content-Type-Options", "nosniff",
"Checks that browsers are told not to guess (sniff) content types.",
"Without nosniff, a browser may execute an uploaded text or image file as script or HTML, enabling XSS through file uploads.",
"Send  X-Content-Type-Options: nosniff  on every response (Apache: Header always set X-Content-Type-Options nosniff; nginx: add_header X-Content-Type-Options nosniff always;).",
check.Low, check.Standards{CWE: []string{"CWE-430"}, OWASP: []string{"A05:2021"}, ASVS: []string{"14.4.4"}, NIST: []string{"CM-6"}})
simpleHeader("WEB-HDR-005", "Missing Referrer-Policy", "Referrer-Policy", "",
"Checks that each site limits what URL information is leaked to other sites in the Referer header.",
"Full URLs can contain session tokens, password-reset links or personal data, which would otherwise be sent to every third-party resource and outbound link.",
"Send  Referrer-Policy: strict-origin-when-cross-origin  (or no-referrer). Never use unsafe-url.",
check.Low, check.Standards{CWE: []string{"CWE-201"}, OWASP: []string{"A05:2021"}, ASVS: []string{"14.4.6"}, NIST: []string{"CM-6"}})
simpleHeader("WEB-HDR-006", "Missing Permissions-Policy", "Permissions-Policy", "",
"Checks that each site restricts powerful browser features (camera, microphone, geolocation) it does not use.",
"Restricting features limits what injected or third-party scripts can do in your visitors' browsers.",
"Send, for example,  Permissions-Policy: camera=(), microphone=(), geolocation=(), payment=()  adjusted to the features the site really uses.",
check.Low, check.Standards{CWE: []string{"CWE-1188"}, OWASP: []string{"A05:2021"}, NIST: []string{"CM-6", "CM-7"}})
151
check.Register(&check.Check{
ID:        "WEB-HDR-007",
Title:     "Server Software Version Disclosed",
Domain:    check.DomainWeb,
Severity:  check.Low,
CVSS:      "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N",
Summary:   "Checks whether response headers reveal exact web server, PHP or framework versions.",
Rationale: "Exact versions let attackers match the site against public exploit lists in seconds. Hiding them does not fix vulnerabilities but removes free reconnaissance.",
Detection: "Looks for a version number in the Server header and for the X-Powered-By, X-AspNet-Version and X-Generator headers.",
Fix:       "Apache: ServerTokens Prod and ServerSignature Off . nginx: server_tokens off; . PHP: expose_php = Off in php.ini . Remove X-Powered-By in the application or proxy.",
Verify:    "curl -sI https://<site>/ | grep -Ei '^(server|x-powered-by)'",
Refs:      []check.Ref{refHTTPHeadersCS, {Title: "Apache HTTP Server, ServerTokens directive", URL: "https://httpd.apache.org/docs/2.4/mod/core.html#servertokens"}},
Standards: check.Standards{CWE: []string{"CWE-497"}, OWASP: []string{"A05:2021"}, ASVS: []string{"14.3.3"}, WSTG: []string{"WSTG-INFO-02"}, NIST: []string{"CM-7", "SI-11"}},
Run: func(ctx context.Context, s sys.System) []check.Result {
	ver := regexp.MustCompile(`\d+\.\d+`)
	return ForEachSite(ctx, s, func(st Site) check.Result {
		if r, skip := st.Redirected(); skip {
			return r
		}
		var ev []string
		if v := st.Home.Header.Get("Server"); ver.MatchString(v) {
			ev = append(ev, "Server: "+v)
		}
		for _, h := range []string{"X-Powered-By", "X-AspNet-Version", "X-AspNetMvc-Version", "X-Generator"} {
			if v := st.Home.Header.Get(h); v != "" {
				ev = append(ev, h+": "+v)
			}
		}
		if len(ev) > 0 {
			return check.FailR(st.Name, "Software versions are disclosed in headers", ev...)
		}
		return check.PassR(st.Name, "No version details in headers")
	})
},
})
187}
188
189func hstsMaxAge(h string) (uint64, bool) {
var value string
for _, part := range strings.Split(h, ";") {
kv := strings.SplitN(strings.TrimSpace(part), "=", 2)
if len(kv) == 2 && strings.EqualFold(strings.TrimSpace(kv[0]), "max-age") {
	if value != "" {
		return 0, false
	}
	value = strings.TrimSpace(kv[1])
}
}
// RFC 6797 allows max-age as a token or a quoted string.
if len(value) >= 2 && strings.HasPrefix(value, "\"") && strings.HasSuffix(value, "\"") {
value = value[1 : len(value)-1]
}
if value == "" {
return 0, false
}
n, err := strconv.ParseUint(value, 10, 64)
return n, err == nil
209}
210
211func weakCSP(h string) string {
dirs := map[string][]string{}
for _, raw := range strings.Split(strings.ToLower(h), ";") {
f := strings.Fields(raw)
if len(f) > 0 {
	dirs[f[0]] = f[1:]
}
}
script := dirs["script-src"]
if len(script) == 0 {
script = dirs["default-src"]
}
for _, src := range script {
if src == "*" || src == "data:" || strings.HasPrefix(src, "http:") {
	return "CSP permits an unsafe script source"
}
if src == "'unsafe-eval'" {
	return "CSP allows unsafe script evaluation"
}
if src == "'unsafe-inline'" && !hasNonceOrHash(script) {
	return "CSP allows inline scripts without a nonce or hash"
}
}
if _, ok := dirs["object-src"]; !ok {
return "CSP does not restrict object-src"
}
return ""
238}
239func hasNonceOrHash(src []string) bool {
for _, s := range src {
if strings.HasPrefix(s, "'nonce-") || strings.HasPrefix(s, "'sha256-") || strings.HasPrefix(s, "'sha384-") || strings.HasPrefix(s, "'sha512-") {
	return true
}
}
return false
246}
247
248// framingRestricted evaluates CSP frame-ancestors first (browsers ignore
249// X-Frame-Options when it is present), then X-Frame-Options.
250func framingRestricted(h http.Header) (bool, string) {
for _, csp := range h.Values("Content-Security-Policy") {
for _, raw := range strings.Split(strings.ToLower(csp), ";") {
	f := strings.Fields(raw)
	if len(f) == 0 || f[0] != "frame-ancestors" {
		continue
	}
	for _, src := range f[1:] {
		if src == "*" || src == "http:" || src == "https:" || src == "*:" {
			return false, "CSP frame-ancestors allows any site to frame the page (" + strings.Join(f[1:], " ") + ")"
		}
	}
	if len(f) == 1 {
		return false, "CSP frame-ancestors has no source list"
	}
	return true, "frame-ancestors " + strings.Join(f[1:], " ")
}
}
var vals []string
for _, v := range h.Values("X-Frame-Options") {
for _, p := range strings.Split(v, ",") {
	if p = strings.ToUpper(strings.TrimSpace(p)); p != "" {
		vals = append(vals, p)
	}
}
}
if len(vals) == 0 {
return false, "Neither X-Frame-Options nor CSP frame-ancestors is set"
}
for _, v := range vals[1:] {
if v != vals[0] {
	return false, "X-Frame-Options has conflicting values (" + strings.Join(vals, ", ") + "), which browsers ignore"
}
}
if vals[0] == "DENY" || vals[0] == "SAMEORIGIN" {
return true, "X-Frame-Options " + vals[0]
}
return false, "X-Frame-Options value " + vals[0] + " is not DENY or SAMEORIGIN"
288}
289
290// unsafeReferrer reports whether the effective Referrer-Policy (the last
291// recognised token, per the W3C Referrer Policy specification) is unsafe-url.
292func unsafeReferrer(vals []string) bool {
last := ""
for _, v := range vals {
for _, t := range strings.Split(v, ",") {
	switch t = strings.ToLower(strings.TrimSpace(t)); t {
	case "no-referrer", "no-referrer-when-downgrade", "same-origin", "origin", "strict-origin", "origin-when-cross-origin", "strict-origin-when-cross-origin", "unsafe-url":
		last = t
	}
}
}
return last == "unsafe-url"
303}

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Cite This Page

If this page helped your work, please cite it. The version and web address are filled in; the access date is today's date in your browser. Every other style, and when credit is required, is on How to Cite OpenVAPT.

APA 7

OpenVAPT. (2026). WEB-HDR-007 Server Software Version Disclosed (Version 0.1.0-alpha.6). OpenVAPT Check Catalogue. Retrieved October 16, 2026, from https://openvapt.com/checks/WEB-HDR-007.html

In text: (OpenVAPT, 2026). Accessed: the date shown is today's date from your own browser (the site's build date without JavaScript); change it to the day you read the page.

BibTeX

@misc{openvapt_web_hdr_007,
  author       = {{OpenVAPT}},
  title        = {{WEB-HDR-007 Server Software Version Disclosed}},
  year         = {2026},
  howpublished = {\url{https://openvapt.com/checks/WEB-HDR-007.html}},
  note         = {OpenVAPT Check Catalogue, version 0.1.0-alpha.6. Accessed 16 October 2026}
}

Accessed: the date shown is today's date from your own browser (the site's build date without JavaScript); change it to the day you read the page.

Citing OpenVAPT does not mean OpenVAPT endorses, approves or has reviewed your work.

Cite This Work: OpenVAPT. (2026). OpenVAPT: An open academic vulnerability assessment tool (Version 0.1.0-alpha.6) [Computer software]. https://github.com/OpenVAPT/openvapt

1	package web
2
3	import (
4	"context"
5	"net/http"
6	"regexp"
7	"strconv"
8	"strings"
9
10	"github.com/openvapt/openvapt/internal/check"
11	"github.com/openvapt/openvapt/internal/sys"
12	)
13
14	func init() {
15	check.Register(&check.Check{
16	ID: "WEB-HDR-001",
17	Title: "Missing HTTP Strict Transport Security (HSTS)",
18	Domain: check.DomainWeb,
19	Severity: check.Medium,
20	CVSS: "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N",
21	Summary: "Checks that HTTPS sites tell browsers to always use HTTPS, for at least six months.",
22	Rationale: "Without HSTS, the first visit or any typed http:// link can be intercepted and downgraded to plain HTTP (SSL stripping) on public Wi-Fi.",
23	Detection: "Reads the Strict-Transport-Security header from each HTTPS site's home page, including a redirect response, because browsers honour HSTS on any HTTPS response. Plain HTTP responses are not evaluated. Missing, or max-age below 15552000 seconds (180 days), fails.",
24	Fix: "Apache: Header always set Strict-Transport-Security \"max-age=31536000; includeSubDomains\" . nginx: add_header Strict-Transport-Security \"max-age=31536000; includeSubDomains\" always; . Only add 'preload' once every subdomain supports HTTPS.",
25	Verify: "curl -sI https://<site>/ \| grep -i strict-transport-security",
26	Refs: []check.Ref{{Title: "RFC 6797, HTTP Strict Transport Security", URL: "https://www.rfc-editor.org/rfc/rfc6797.html"}, refHTTPHeadersCS, refMDN("Strict-Transport-Security")},
27	Standards: check.Standards{CWE: []string{"CWE-319", "CWE-523"}, OWASP: []string{"A05:2021"}, ASVS: []string{"14.4.5"}, WSTG: []string{"WSTG-CONF-07"}, NIST: []string{"SC-8"}},
28	Run: func(ctx context.Context, s sys.System) []check.Result {
29	return ForEachSite(ctx, s, func(st Site) check.Result {
30	// Browsers honour HSTS on any HTTPS response, redirects
31	// included (RFC 6797 section 8.1), so a 3xx is evaluated too.
32	if !st.HTTPS {
33	return check.SkipR(st.Name, "Site not served over HTTPS (see WEB-TLS-001)")
34	}
35	h := st.Home.Header.Get("Strict-Transport-Security")
36	if h == "" {
37	return check.FailR(st.Name, "Strict-Transport-Security header is missing")
38	}
39	n, ok := hstsMaxAge(h)
40	if !ok {
41	return check.FailR(st.Name, "HSTS max-age is missing, duplicated or invalid", h)
42	}
43	if n < 15552000 {
44	return check.FailR(st.Name, "HSTS max-age is shorter than 180 days", h)
45	}
46	return check.PassR(st.Name, "HSTS is set", h)
47	})
48	},
49	})
50
51	check.Register(&check.Check{
52	ID: "WEB-HDR-002",
53	Title: "Missing Content Security Policy",
54	Domain: check.DomainWeb,
55	Severity: check.Medium,
56	CVSS: "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
57	Summary: "Checks that each site sends a Content-Security-Policy header.",
58	Rationale: "A CSP limits where scripts may load from, turning many cross-site scripting (XSS) bugs from account takeover into a blocked request.",
59	Detection: "Reads Content-Security-Policy from each site's home page. Missing fails. A policy containing 'unsafe-inline' in script-src (without a nonce or hash) or a bare * source is reported as weak.",
60	Fix: "Start with a report-only policy to find what the site loads, then enforce, for example: Content-Security-Policy: default-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'self'",
61	Verify: "curl -sI https://<site>/ \| grep -i content-security-policy",
62	Refs: []check.Ref{{Title: "OWASP Content Security Policy Cheat Sheet", URL: "https://cheatsheetseries.owasp.org/cheatsheets/Content_Security_Policy_Cheat_Sheet.html"}, {Title: "W3C Content Security Policy Level 3", URL: "https://www.w3.org/TR/CSP3/"}},
63	Standards: check.Standards{CWE: []string{"CWE-1021", "CWE-79"}, OWASP: []string{"A03:2021", "A05:2021"}, ASVS: []string{"14.4.3"}, WSTG: []string{"WSTG-CONF-12"}, NIST: []string{"SI-10"}},
64	Run: func(ctx context.Context, s sys.System) []check.Result {
65	return ForEachSite(ctx, s, func(st Site) check.Result {
66	if r, skip := st.Redirected(); skip {
67	return r
68	}
69	h := st.Home.Header.Get("Content-Security-Policy")
70	if h == "" {
71	return check.FailR(st.Name, "Content-Security-Policy header is missing")
72	}
73	if reason := weakCSP(h); reason != "" {
74	return check.FailR(st.Name, reason, h)
75	}
76	return check.PassR(st.Name, "Content-Security-Policy is set", h)
77	})
78	},
79	})
80
81	check.Register(&check.Check{
82	ID: "WEB-HDR-003",
83	Title: "Site Can Be Framed (Clickjacking)",
84	Domain: check.DomainWeb,
85	Severity: check.Medium,
86	CVSS: "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N",
87	Summary: "Checks that each site forbids being embedded in other sites' frames.",
88	Rationale: "If a page can be framed, an attacker can overlay it invisibly and trick users into clicking buttons (clickjacking), such as 'delete' or 'transfer'.",
89	Detection: "Passes if the CSP frame-ancestors directive restricts framing (a * or scheme-only source fails), or, without frame-ancestors, X-Frame-Options is DENY or SAMEORIGIN (repeated identical values are accepted; conflicting values fail).",
90	Fix: "Send Content-Security-Policy: frame-ancestors 'self' (modern) and X-Frame-Options: SAMEORIGIN (older browsers).",
91	Verify: "curl -sI https://<site>/ \| grep -Ei 'x-frame-options\|frame-ancestors'",
92	Refs: []check.Ref{{Title: "OWASP Clickjacking Defense Cheat Sheet", URL: "https://cheatsheetseries.owasp.org/cheatsheets/Clickjacking_Defense_Cheat_Sheet.html"}, refMDN("X-Frame-Options")},
93	Standards: check.Standards{CWE: []string{"CWE-1021"}, OWASP: []string{"A04:2021"}, ASVS: []string{"14.4.7"}, WSTG: []string{"WSTG-CLNT-09"}, NIST: []string{"SC-18"}},
94	Run: func(ctx context.Context, s sys.System) []check.Result {
95	return ForEachSite(ctx, s, func(st Site) check.Result {
96	if r, skip := st.Redirected(); skip {
97	return r
98	}
99	ok, why := framingRestricted(st.Home.Header)
100	if ok {
101	return check.PassR(st.Name, "Framing is restricted", why)
102	}
103	return check.FailR(st.Name, why)
104	})
105	},
106	})
107
108	simpleHeader := func(id, title, header, want, summary, rationale, fix string, sev check.Severity, std check.Standards) {
109	check.Register(&check.Check{
110	ID: id, Title: title, Domain: check.DomainWeb, Severity: sev,
111	CVSS: "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N",
112	Summary: summary,
113	Rationale: rationale,
114	Detection: "Reads the " + header + " header from each site's home page and checks that it is present" + map[bool]string{true: " with the value " + want, false: ""}[want != ""] + ".",
115	Fix: fix,
116	Verify: "curl -sI https://<site>/ \| grep -i " + strings.ToLower(header),
117	Refs: []check.Ref{refSecureHeaders, refMDN(header)},
118	Standards: std,
119	Run: func(ctx context.Context, s sys.System) []check.Result {
120	return ForEachSite(ctx, s, func(st Site) check.Result {
121	if r, skip := st.Redirected(); skip {
122	return r
123	}
124	v := st.Home.Header.Get(header)
125	if v == "" \|\| (want != "" && !strings.EqualFold(strings.TrimSpace(v), want)) {
126	return check.FailR(st.Name, header+" is missing or not '"+want+"'", v)
127	}
128	if header == "Referrer-Policy" && unsafeReferrer(st.Home.Header.Values(header)) {
129	return check.FailR(st.Name, "Referrer-Policy unsafe-url sends the full URL to every site", v)
130	}
131	return check.PassR(st.Name, header+" is set", v)
132	})
133	},
134	})
135	}
136	simpleHeader("WEB-HDR-004", "Missing X-Content-Type-Options", "X-Content-Type-Options", "nosniff",
137	"Checks that browsers are told not to guess (sniff) content types.",
138	"Without nosniff, a browser may execute an uploaded text or image file as script or HTML, enabling XSS through file uploads.",
139	"Send X-Content-Type-Options: nosniff on every response (Apache: Header always set X-Content-Type-Options nosniff; nginx: add_header X-Content-Type-Options nosniff always;).",
140	check.Low, check.Standards{CWE: []string{"CWE-430"}, OWASP: []string{"A05:2021"}, ASVS: []string{"14.4.4"}, NIST: []string{"CM-6"}})
141	simpleHeader("WEB-HDR-005", "Missing Referrer-Policy", "Referrer-Policy", "",
142	"Checks that each site limits what URL information is leaked to other sites in the Referer header.",
143	"Full URLs can contain session tokens, password-reset links or personal data, which would otherwise be sent to every third-party resource and outbound link.",
144	"Send Referrer-Policy: strict-origin-when-cross-origin (or no-referrer). Never use unsafe-url.",
145	check.Low, check.Standards{CWE: []string{"CWE-201"}, OWASP: []string{"A05:2021"}, ASVS: []string{"14.4.6"}, NIST: []string{"CM-6"}})
146	simpleHeader("WEB-HDR-006", "Missing Permissions-Policy", "Permissions-Policy", "",
147	"Checks that each site restricts powerful browser features (camera, microphone, geolocation) it does not use.",
148	"Restricting features limits what injected or third-party scripts can do in your visitors' browsers.",
149	"Send, for example, Permissions-Policy: camera=(), microphone=(), geolocation=(), payment=() adjusted to the features the site really uses.",
150	check.Low, check.Standards{CWE: []string{"CWE-1188"}, OWASP: []string{"A05:2021"}, NIST: []string{"CM-6", "CM-7"}})
151
152	check.Register(&check.Check{
153	ID: "WEB-HDR-007",
154	Title: "Server Software Version Disclosed",
155	Domain: check.DomainWeb,
156	Severity: check.Low,
157	CVSS: "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N",
158	Summary: "Checks whether response headers reveal exact web server, PHP or framework versions.",
159	Rationale: "Exact versions let attackers match the site against public exploit lists in seconds. Hiding them does not fix vulnerabilities but removes free reconnaissance.",
160	Detection: "Looks for a version number in the Server header and for the X-Powered-By, X-AspNet-Version and X-Generator headers.",
161	Fix: "Apache: ServerTokens Prod and ServerSignature Off . nginx: server_tokens off; . PHP: expose_php = Off in php.ini . Remove X-Powered-By in the application or proxy.",
162	Verify: "curl -sI https://<site>/ \| grep -Ei '^(server\|x-powered-by)'",
163	Refs: []check.Ref{refHTTPHeadersCS, {Title: "Apache HTTP Server, ServerTokens directive", URL: "https://httpd.apache.org/docs/2.4/mod/core.html#servertokens"}},
164	Standards: check.Standards{CWE: []string{"CWE-497"}, OWASP: []string{"A05:2021"}, ASVS: []string{"14.3.3"}, WSTG: []string{"WSTG-INFO-02"}, NIST: []string{"CM-7", "SI-11"}},
165	Run: func(ctx context.Context, s sys.System) []check.Result {
166	ver := regexp.MustCompile(`\d+\.\d+`)
167	return ForEachSite(ctx, s, func(st Site) check.Result {
168	if r, skip := st.Redirected(); skip {
169	return r
170	}
171	var ev []string
172	if v := st.Home.Header.Get("Server"); ver.MatchString(v) {
173	ev = append(ev, "Server: "+v)
174	}
175	for _, h := range []string{"X-Powered-By", "X-AspNet-Version", "X-AspNetMvc-Version", "X-Generator"} {
176	if v := st.Home.Header.Get(h); v != "" {
177	ev = append(ev, h+": "+v)
178	}
179	}
180	if len(ev) > 0 {
181	return check.FailR(st.Name, "Software versions are disclosed in headers", ev...)
182	}
183	return check.PassR(st.Name, "No version details in headers")
184	})
185	},
186	})
187	}
188
189	func hstsMaxAge(h string) (uint64, bool) {
190	var value string
191	for _, part := range strings.Split(h, ";") {
192	kv := strings.SplitN(strings.TrimSpace(part), "=", 2)
193	if len(kv) == 2 && strings.EqualFold(strings.TrimSpace(kv[0]), "max-age") {
194	if value != "" {
195	return 0, false
196	}
197	value = strings.TrimSpace(kv[1])
198	}
199	}
200	// RFC 6797 allows max-age as a token or a quoted string.
201	if len(value) >= 2 && strings.HasPrefix(value, "\"") && strings.HasSuffix(value, "\"") {
202	value = value[1 : len(value)-1]
203	}
204	if value == "" {
205	return 0, false
206	}
207	n, err := strconv.ParseUint(value, 10, 64)
208	return n, err == nil
209	}
210
211	func weakCSP(h string) string {
212	dirs := map[string][]string{}
213	for _, raw := range strings.Split(strings.ToLower(h), ";") {
214	f := strings.Fields(raw)
215	if len(f) > 0 {
216	dirs[f[0]] = f[1:]
217	}
218	}
219	script := dirs["script-src"]
220	if len(script) == 0 {
221	script = dirs["default-src"]
222	}
223	for _, src := range script {
224	if src == "*" \|\| src == "data:" \|\| strings.HasPrefix(src, "http:") {
225	return "CSP permits an unsafe script source"
226	}
227	if src == "'unsafe-eval'" {
228	return "CSP allows unsafe script evaluation"
229	}
230	if src == "'unsafe-inline'" && !hasNonceOrHash(script) {
231	return "CSP allows inline scripts without a nonce or hash"
232	}
233	}
234	if _, ok := dirs["object-src"]; !ok {
235	return "CSP does not restrict object-src"
236	}
237	return ""
238	}
239	func hasNonceOrHash(src []string) bool {
240	for _, s := range src {
241	if strings.HasPrefix(s, "'nonce-") \|\| strings.HasPrefix(s, "'sha256-") \|\| strings.HasPrefix(s, "'sha384-") \|\| strings.HasPrefix(s, "'sha512-") {
242	return true
243	}
244	}
245	return false
246	}
247
248	// framingRestricted evaluates CSP frame-ancestors first (browsers ignore
249	// X-Frame-Options when it is present), then X-Frame-Options.
250	func framingRestricted(h http.Header) (bool, string) {
251	for _, csp := range h.Values("Content-Security-Policy") {
252	for _, raw := range strings.Split(strings.ToLower(csp), ";") {
253	f := strings.Fields(raw)
254	if len(f) == 0 \|\| f[0] != "frame-ancestors" {
255	continue
256	}
257	for _, src := range f[1:] {
258	if src == "" \|\| src == "http:" \|\| src == "https:" \|\| src == ":" {
259	return false, "CSP frame-ancestors allows any site to frame the page (" + strings.Join(f[1:], " ") + ")"
260	}
261	}
262	if len(f) == 1 {
263	return false, "CSP frame-ancestors has no source list"
264	}
265	return true, "frame-ancestors " + strings.Join(f[1:], " ")
266	}
267	}
268	var vals []string
269	for _, v := range h.Values("X-Frame-Options") {
270	for _, p := range strings.Split(v, ",") {
271	if p = strings.ToUpper(strings.TrimSpace(p)); p != "" {
272	vals = append(vals, p)
273	}
274	}
275	}
276	if len(vals) == 0 {
277	return false, "Neither X-Frame-Options nor CSP frame-ancestors is set"
278	}
279	for _, v := range vals[1:] {
280	if v != vals[0] {
281	return false, "X-Frame-Options has conflicting values (" + strings.Join(vals, ", ") + "), which browsers ignore"
282	}
283	}
284	if vals[0] == "DENY" \|\| vals[0] == "SAMEORIGIN" {
285	return true, "X-Frame-Options " + vals[0]
286	}
287	return false, "X-Frame-Options value " + vals[0] + " is not DENY or SAMEORIGIN"
288	}
289
290	// unsafeReferrer reports whether the effective Referrer-Policy (the last
291	// recognised token, per the W3C Referrer Policy specification) is unsafe-url.
292	func unsafeReferrer(vals []string) bool {
293	last := ""
294	for _, v := range vals {
295	for _, t := range strings.Split(v, ",") {
296	switch t = strings.ToLower(strings.TrimSpace(t)); t {
297	case "no-referrer", "no-referrer-when-downgrade", "same-origin", "origin", "strict-origin", "origin-when-cross-origin", "strict-origin-when-cross-origin", "unsafe-url":
298	last = t
299	}
300	}
301	}
302	return last == "unsafe-url"
303	}