---
title: "HOST-KRN-025 IPv6 Router Advertisements Accepted"
canonical: https://openvapt.com/checks/HOST-KRN-025.html
html: https://openvapt.com/checks/HOST-KRN-025.html
site: OpenVAPT, https://openvapt.com/
license: OpenVAPT Source-Available Licence 1.3, https://openvapt.com/legal/licence-text.html
modified: 2026-10-14
version: 0.1.0-alpha.6
---

# HOST-KRN-025 IPv6 Router Advertisements Accepted

Checks that the server does not reconfigure its IPv6 addresses and routes from router advertisements.

- Domain: Server
- Severity: Low
- Control category: Secure Configuration
- Fix effort: low
- CVSS v3.1 vector: `CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N`
- CIS Controls v8: 4.1
- NIST CSF 2.0: PR.PS-01
- CWE: CWE-940
- NIST SP 800-53 Rev. 5: SC-7, CM-6
- Benchmark topic: Kernel parameters: net.ipv6.conf.all.accept_ra (topic only, no benchmark text)

## Why It Matters

A rogue router advertisement on the local network can add a default route through an attacker's machine or assign addresses that bypass firewall rules; servers use static addressing.

## How It Detects

Reads /proc/sys/net/ipv6/conf/*/accept_ra directly (all, default and every interface; no command is run) and fails if any of them differs from the hardened value 0. Passes with a note when IPv6 forwarding is off and /proc/net/ipv6_route shows a default route learned from a router advertisement (RTF_DEFAULT or RTF_ADDRCONF flag), because turning advertisements off would remove that route.

## How to Fix

Create /etc/sysctl.d/60-openvapt-hardening.conf containing:  net.ipv6.conf.all.accept_ra = 0  then apply with: sysctl --system. Caution: on a host that gets its IPv6 address or default route from router advertisements (SLAAC, most cloud dual-stack VMs), accept_ra = 0 removes the IPv6 default route and cuts IPv6 connectivity. Use it only with static IPv6 addressing; otherwise keep accept_ra = 1 and rely on RA Guard on the switch or a host firewall rule for RA sources.

## How to Verify

```
sysctl net.ipv6.conf.all.accept_ra  should print 0.
```

## Learn the Theory

- [P1 Linux Server Hardening](https://openvapt.com/academy/p1.md)
- [P17 Kernel, Filesystem and Boot Hardening](https://openvapt.com/academy/p17.md)

## References

- [Linux kernel documentation, IP sysctl](https://docs.kernel.org/networking/ip-sysctl.html)

## Source Code

https://github.com/OpenVAPT/openvapt/blob/574f7f3333c44b75a3c649e2d93a76d507f75adf/internal/checks/host/kernel.go

Run it: `openvapt scan --only HOST-KRN-025`. Read it offline: `openvapt explain HOST-KRN-025`.

---

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