# CVE-2026-74561: nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush

> A race condition in the Linux kernel nexthop module allows a use-after-free, potentially leading to system crashes or arbitrary code execution.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2026-74561, DEBIAN-CVE-2026-74561, GHSA-x2q4-hjx7-v4h6, UBUNTU-CVE-2026-74561

## What is CVE-2026-74561?

CVE-2026-74561 is a high-severity use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush

nh_rt_cache_flush() walks nh->f6i_list during an RTNL-serialized nexthop
replace without holding nh->lock, racing the unlocked IPv6 route
add/delete that mutate the list under nh->lock and free fib6_info
entries (nh_rt_cache_flush() is inlined into rtm_new_nexthop()):

  BUG: KASAN: slab-use-after-free in nh_rt_cache_flush (net/ipv4/nexthop.c:2243)
  Read of size 8 at addr ffff888012953e18 by task exploit/146
   nh_rt_cache_flush (net/ipv4/nexthop.c:2243)
   replace_nexthop (net/ipv4/nexthop.c:2610)
   rtm_new_nexthop (net/ipv4/nexthop.c:3323)
   rtnetlink_rcv_msg (net/core/rtnetlink.c:7076)

Unlike the other f6i_list walks, this one bumps each route's sernum via
fib6_update_sernum_upto_root(), which needs tb6_lock; taking nh->lock
around it would invert the established tb6_lock -> nh->lock order and
deadlock. As the only purpose is to invalidate cached dsts, bump the
IPv6 sernum for the whole netns with rt_genid_bump_ipv6() instead,
mirroring the rt_cache_flush() already done for IPv4 just above.

## Which versions are affected by CVE-2026-74561?


## How do I fix CVE-2026-74561?

Apply the vendor's patch.

## Is CVE-2026-74561 being exploited?

There is no known exploitation of CVE-2026-74561 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74561 and fix it if it is affected.

What it is: CVE-2026-74561 is a high-severity use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74561 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74561/ (Markdown: https://insights.sbomify.com/CVE-2026-74561/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74561
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74561
- OSV: https://osv.dev/vulnerability/CVE-2026-74561

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74561/
Summaries are generated and may contain mistakes; the official description above is the record.