MediumNET-TLS-004Cryptography and TLSNetwork

Weak TLS 1.2 Cipher Suites Accepted

A local TLS service accepts an RC4, 3DES, or CBC with SHA-1 cipher suite under TLS 1.2.

Why It Matters: Obsolete cipher constructions lack modern authenticated encryption and are prohibited by current TLS hardening guidance.
How It Detects: Offers restricted TLS 1.2 cipher lists to loopback services. A successful handshake proves the weak suite is accepted. Go does not implement NULL, EXPORT, or anonymous suites, so those cannot be actively offered and remain a documented limitation.
How to Fix: Allow only modern AEAD suites for TLS 1.2 and prefer TLS 1.3. Remove RC4, 3DES, NULL, EXPORT, anonymous, and CBC with SHA-1 suites. Caution: very old clients and devices that support only those suites stop connecting; check the access logs for them first.
How to Verify: Use an approved local TLS scanner and confirm each prohibited TLS 1.2 suite is rejected. Implicit TLS mail ports 465, 993, and 995 are included; STARTTLS is out of scope.
CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
Control Category: Cryptography and TLS: CIS Controls v8 3; NIST CSF 2.0 PR.DS
Fix Effort: Low
CIS Controls v8 Safeguard: 3.10
NIST CSF 2.0 Subcategory: PR.DS-02
OWASP WSTG v4.2: WSTG-CRYP-01
CWE: CWE-326, CWE-327
OWASP Top 10: A02:2021
OWASP ASVS 4.0.3: 9.1.3
NIST SP 800-53 Rev. 5: SC-8, SC-13
References: RFC 8996, Deprecating TLS 1.0 and TLS 1.1
NIST SP 800-52 Rev. 2, Guidelines for TLS Implementations
Mozilla Server Side TLS guidelines

Learn the theory behind this check: P4 TLS, Certificates and HTTPS.

Source Code

The complete file that defines this check. Run it with openvapt scan --only NET-TLS-004, or read it offline with openvapt explain NET-TLS-004.

internal/checks/network/tls_depth.go · Lines 1-116View on GitHub at This Commit

1package network
2
3import (
"context"
"crypto/tls"
"fmt"
"strings"
8
"github.com/openvapt/openvapt/internal/check"
"github.com/openvapt/openvapt/internal/sys"
11)
12
13func init() {
check.Register(&check.Check{
ID:        "NET-TLS-004",
Title:     "Weak TLS 1.2 Cipher Suites Accepted",
Domain:    check.DomainNetwork,
Severity:  check.Medium,
Category:  check.CatCrypto,
Effort:    check.EffortLow,
CVSS:      "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N",
Summary:   "A local TLS service accepts an RC4, 3DES, or CBC with SHA-1 cipher suite under TLS 1.2.",
Rationale: "Obsolete cipher constructions lack modern authenticated encryption and are prohibited by current TLS hardening guidance.",
Detection: "Offers restricted TLS 1.2 cipher lists to loopback services. A successful handshake proves the weak suite is accepted. Go does not implement NULL, EXPORT, or anonymous suites, so those cannot be actively offered and remain a documented limitation.",
Fix:       "Allow only modern AEAD suites for TLS 1.2 and prefer TLS 1.3. Remove RC4, 3DES, NULL, EXPORT, anonymous, and CBC with SHA-1 suites. Caution: very old clients and devices that support only those suites stop connecting; check the access logs for them first.",
Verify:    "Use an approved local TLS scanner and confirm each prohibited TLS 1.2 suite is rejected. Implicit TLS mail ports 465, 993, and 995 are included; STARTTLS is out of scope.",
Refs:      refTLS,
Standards: check.Standards{CWE: []string{"CWE-326", "CWE-327"}, OWASP: []string{"A02:2021"}, WSTG: []string{"WSTG-CRYP-01"}, ASVS: []string{"9.1.3"}, NIST: []string{"SC-8", "SC-13"}},
Run: func(ctx context.Context, s sys.System) []check.Result {
	targets := tlsTargets(s)
	if len(targets) == 0 {
		return []check.Result{check.SkipR("TLS", "No local implicit TLS service was found")}
	}
	weak := []uint16{tls.TLS_RSA_WITH_RC4_128_SHA, tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA, tls.TLS_RSA_WITH_AES_128_CBC_SHA, tls.TLS_RSA_WITH_AES_256_CBC_SHA, tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA}
	var out []check.Result
	for _, t := range targets {
		target := t[1] + " on port " + t[0]
		accepted := []string{}
		for _, suite := range weak {
			if info, err := s.TLSWithCiphers(ctx, t[0], t[1], []uint16{suite}); err == nil {
				accepted = append(accepted, tls.CipherSuiteName(info.Cipher))
			}
		}
		if len(accepted) > 0 {
			out = append(out, check.FailR(target, "Weak TLS 1.2 cipher suite accepted", accepted...))
		} else {
			out = append(out, check.PassR(target, "Testable weak TLS 1.2 cipher suites were rejected"))
		}
	}
	return out
}})
check.Register(&check.Check{
ID:        "NET-TLS-005",
Title:     "TLS Certificate Public Key Too Small",
Domain:    check.DomainNetwork,
Severity:  check.Medium,
Category:  check.CatCrypto,
Effort:    check.EffortMedium,
CVSS:      "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N",
Summary:   "A TLS leaf certificate uses RSA below 2048 bits or an elliptic curve below 256 bits.",
Rationale: "Undersized public keys provide inadequate security strength and may permit certificate impersonation as cryptanalytic capability improves.",
Detection: "Reads the leaf public key from loopback TLS handshakes and measures RSA modulus or elliptic curve size.",
Fix:       "Replace the certificate and private key with RSA 2048 bits or stronger, or an approved EC key of at least 256 bits.",
Verify:    "Inspect the renewed leaf certificate key size on ports 443, 465, 993, 995, 8443, and 10000. STARTTLS is out of scope.",
Refs:      []check.Ref{{Title: "NIST SP 800-131A Rev. 2, Transitioning the Use of Cryptographic Algorithms and Key Lengths", URL: "https://csrc.nist.gov/pubs/sp/800/131/a/r2/final"}},
Standards: check.Standards{CWE: []string{"CWE-326"}, OWASP: []string{"A02:2021"}, WSTG: []string{"WSTG-CRYP-01"}, NIST: []string{"SC-12", "SC-13"}},
Run: certDepthRun(func(i sys.TLSInfo) bool {
	return strings.EqualFold(i.PublicKeyAlgorithm, "RSA") && i.PublicKeyBits < 2048 || (strings.EqualFold(i.PublicKeyAlgorithm, "ECDSA") || strings.Contains(strings.ToLower(i.PublicKeyAlgorithm), "elliptic")) && i.PublicKeyBits < 256
}, "Leaf certificate public key is too small")})
check.Register(&check.Check{
ID:        "NET-TLS-006",
Title:     "SHA-1 Signed TLS Leaf Certificate",
Domain:    check.DomainNetwork,
Severity:  check.Medium,
Category:  check.CatCrypto,
Effort:    check.EffortMedium,
CVSS:      "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N",
Summary:   "A TLS leaf certificate is signed using SHA-1.",
Rationale: "SHA-1 collision attacks invalidate its use for digital signatures and modern clients reject SHA-1 certificates.",
Detection: "Reads the leaf certificate signature algorithm from loopback implicit TLS handshakes and flags SHA-1.",
Fix:       "Reissue the certificate with SHA-256 or stronger and deploy the complete updated chain.",
Verify:    "Inspect the signature algorithm on each implicit TLS service. STARTTLS is out of scope.",
Refs:      []check.Ref{{Title: "NIST Transitioning Away from SHA-1", URL: "https://csrc.nist.gov/News/2022/nist-transitioning-away-from-sha-1-for-all-apps"}},
Standards: check.Standards{CWE: []string{"CWE-327"}, OWASP: []string{"A02:2021"}, WSTG: []string{"WSTG-CRYP-01"}, NIST: []string{"SC-12", "SC-13"}},
Run: certDepthRun(func(i sys.TLSInfo) bool {
	return strings.Contains(strings.ToLower(i.SignatureAlgorithm), "sha-1") || strings.Contains(strings.ToLower(i.SignatureAlgorithm), "sha1")
}, "Leaf certificate uses a SHA-1 signature")})
88}
89
90func certDepthRun(bad func(sys.TLSInfo) bool, msg string) func(context.Context, sys.System) []check.Result {
return func(ctx context.Context, s sys.System) []check.Result {
targets := tlsTargets(s)
if len(targets) == 0 {
	return []check.Result{check.SkipR("TLS", "No local implicit TLS service was found")}
}
var out []check.Result
for _, t := range targets {
	target := t[1] + " on port " + t[0]
	i, err := s.TLS(ctx, t[0], t[1], tls.VersionTLS12, tls.VersionTLS13)
	if err != nil {
		out = append(out, check.IncompleteR(target, "TLS certificate could not be read"))
		continue
	}
	if i.PublicKeyBits == 0 || i.SignatureAlgorithm == "" {
		out = append(out, check.IncompleteR(target, "Certificate key or signature metadata was unavailable"))
		continue
	}
	if bad(i) {
		out = append(out, check.FailR(target, msg, fmt.Sprintf("key %s %d bits, signature %s", i.PublicKeyAlgorithm, i.PublicKeyBits, i.SignatureAlgorithm)))
	} else {
		out = append(out, check.PassR(target, "Certificate key strength and signature metadata passed this check"))
	}
}
return out
}
116}

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APA 7

OpenVAPT. (2026). NET-TLS-004 Weak TLS 1.2 Cipher Suites Accepted (Version 0.1.0-alpha.6). OpenVAPT Check Catalogue. Retrieved October 16, 2026, from https://openvapt.com/checks/NET-TLS-004.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_net_tls_004,
  author       = {{OpenVAPT}},
  title        = {{NET-TLS-004 Weak TLS 1.2 Cipher Suites Accepted}},
  year         = {2026},
  howpublished = {\url{https://openvapt.com/checks/NET-TLS-004.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 network
2
3	import (
4	"context"
5	"crypto/tls"
6	"fmt"
7	"strings"
8
9	"github.com/openvapt/openvapt/internal/check"
10	"github.com/openvapt/openvapt/internal/sys"
11	)
12
13	func init() {
14	check.Register(&check.Check{
15	ID: "NET-TLS-004",
16	Title: "Weak TLS 1.2 Cipher Suites Accepted",
17	Domain: check.DomainNetwork,
18	Severity: check.Medium,
19	Category: check.CatCrypto,
20	Effort: check.EffortLow,
21	CVSS: "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N",
22	Summary: "A local TLS service accepts an RC4, 3DES, or CBC with SHA-1 cipher suite under TLS 1.2.",
23	Rationale: "Obsolete cipher constructions lack modern authenticated encryption and are prohibited by current TLS hardening guidance.",
24	Detection: "Offers restricted TLS 1.2 cipher lists to loopback services. A successful handshake proves the weak suite is accepted. Go does not implement NULL, EXPORT, or anonymous suites, so those cannot be actively offered and remain a documented limitation.",
25	Fix: "Allow only modern AEAD suites for TLS 1.2 and prefer TLS 1.3. Remove RC4, 3DES, NULL, EXPORT, anonymous, and CBC with SHA-1 suites. Caution: very old clients and devices that support only those suites stop connecting; check the access logs for them first.",
26	Verify: "Use an approved local TLS scanner and confirm each prohibited TLS 1.2 suite is rejected. Implicit TLS mail ports 465, 993, and 995 are included; STARTTLS is out of scope.",
27	Refs: refTLS,
28	Standards: check.Standards{CWE: []string{"CWE-326", "CWE-327"}, OWASP: []string{"A02:2021"}, WSTG: []string{"WSTG-CRYP-01"}, ASVS: []string{"9.1.3"}, NIST: []string{"SC-8", "SC-13"}},
29	Run: func(ctx context.Context, s sys.System) []check.Result {
30	targets := tlsTargets(s)
31	if len(targets) == 0 {
32	return []check.Result{check.SkipR("TLS", "No local implicit TLS service was found")}
33	}
34	weak := []uint16{tls.TLS_RSA_WITH_RC4_128_SHA, tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA, tls.TLS_RSA_WITH_AES_128_CBC_SHA, tls.TLS_RSA_WITH_AES_256_CBC_SHA, tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA}
35	var out []check.Result
36	for _, t := range targets {
37	target := t[1] + " on port " + t[0]
38	accepted := []string{}
39	for _, suite := range weak {
40	if info, err := s.TLSWithCiphers(ctx, t[0], t[1], []uint16{suite}); err == nil {
41	accepted = append(accepted, tls.CipherSuiteName(info.Cipher))
42	}
43	}
44	if len(accepted) > 0 {
45	out = append(out, check.FailR(target, "Weak TLS 1.2 cipher suite accepted", accepted...))
46	} else {
47	out = append(out, check.PassR(target, "Testable weak TLS 1.2 cipher suites were rejected"))
48	}
49	}
50	return out
51	}})
52	check.Register(&check.Check{
53	ID: "NET-TLS-005",
54	Title: "TLS Certificate Public Key Too Small",
55	Domain: check.DomainNetwork,
56	Severity: check.Medium,
57	Category: check.CatCrypto,
58	Effort: check.EffortMedium,
59	CVSS: "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N",
60	Summary: "A TLS leaf certificate uses RSA below 2048 bits or an elliptic curve below 256 bits.",
61	Rationale: "Undersized public keys provide inadequate security strength and may permit certificate impersonation as cryptanalytic capability improves.",
62	Detection: "Reads the leaf public key from loopback TLS handshakes and measures RSA modulus or elliptic curve size.",
63	Fix: "Replace the certificate and private key with RSA 2048 bits or stronger, or an approved EC key of at least 256 bits.",
64	Verify: "Inspect the renewed leaf certificate key size on ports 443, 465, 993, 995, 8443, and 10000. STARTTLS is out of scope.",
65	Refs: []check.Ref{{Title: "NIST SP 800-131A Rev. 2, Transitioning the Use of Cryptographic Algorithms and Key Lengths", URL: "https://csrc.nist.gov/pubs/sp/800/131/a/r2/final"}},
66	Standards: check.Standards{CWE: []string{"CWE-326"}, OWASP: []string{"A02:2021"}, WSTG: []string{"WSTG-CRYP-01"}, NIST: []string{"SC-12", "SC-13"}},
67	Run: certDepthRun(func(i sys.TLSInfo) bool {
68	return strings.EqualFold(i.PublicKeyAlgorithm, "RSA") && i.PublicKeyBits < 2048 \|\| (strings.EqualFold(i.PublicKeyAlgorithm, "ECDSA") \|\| strings.Contains(strings.ToLower(i.PublicKeyAlgorithm), "elliptic")) && i.PublicKeyBits < 256
69	}, "Leaf certificate public key is too small")})
70	check.Register(&check.Check{
71	ID: "NET-TLS-006",
72	Title: "SHA-1 Signed TLS Leaf Certificate",
73	Domain: check.DomainNetwork,
74	Severity: check.Medium,
75	Category: check.CatCrypto,
76	Effort: check.EffortMedium,
77	CVSS: "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N",
78	Summary: "A TLS leaf certificate is signed using SHA-1.",
79	Rationale: "SHA-1 collision attacks invalidate its use for digital signatures and modern clients reject SHA-1 certificates.",
80	Detection: "Reads the leaf certificate signature algorithm from loopback implicit TLS handshakes and flags SHA-1.",
81	Fix: "Reissue the certificate with SHA-256 or stronger and deploy the complete updated chain.",
82	Verify: "Inspect the signature algorithm on each implicit TLS service. STARTTLS is out of scope.",
83	Refs: []check.Ref{{Title: "NIST Transitioning Away from SHA-1", URL: "https://csrc.nist.gov/News/2022/nist-transitioning-away-from-sha-1-for-all-apps"}},
84	Standards: check.Standards{CWE: []string{"CWE-327"}, OWASP: []string{"A02:2021"}, WSTG: []string{"WSTG-CRYP-01"}, NIST: []string{"SC-12", "SC-13"}},
85	Run: certDepthRun(func(i sys.TLSInfo) bool {
86	return strings.Contains(strings.ToLower(i.SignatureAlgorithm), "sha-1") \|\| strings.Contains(strings.ToLower(i.SignatureAlgorithm), "sha1")
87	}, "Leaf certificate uses a SHA-1 signature")})
88	}
89
90	func certDepthRun(bad func(sys.TLSInfo) bool, msg string) func(context.Context, sys.System) []check.Result {
91	return func(ctx context.Context, s sys.System) []check.Result {
92	targets := tlsTargets(s)
93	if len(targets) == 0 {
94	return []check.Result{check.SkipR("TLS", "No local implicit TLS service was found")}
95	}
96	var out []check.Result
97	for _, t := range targets {
98	target := t[1] + " on port " + t[0]
99	i, err := s.TLS(ctx, t[0], t[1], tls.VersionTLS12, tls.VersionTLS13)
100	if err != nil {
101	out = append(out, check.IncompleteR(target, "TLS certificate could not be read"))
102	continue
103	}
104	if i.PublicKeyBits == 0 \|\| i.SignatureAlgorithm == "" {
105	out = append(out, check.IncompleteR(target, "Certificate key or signature metadata was unavailable"))
106	continue
107	}
108	if bad(i) {
109	out = append(out, check.FailR(target, msg, fmt.Sprintf("key %s %d bits, signature %s", i.PublicKeyAlgorithm, i.PublicKeyBits, i.SignatureAlgorithm)))
110	} else {
111	out = append(out, check.PassR(target, "Certificate key strength and signature metadata passed this check"))
112	}
113	}
114	return out
115	}
116	}