# CVE-2026-99139: tcp: fix use-after-free in do_tcp_getsockopt(TCP_CONGESTION)


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** AZL-111263, BELL-CVE-2026-99139, DEBIAN-CVE-2026-99139, GHSA-48cq-p2fm-8444, UBUNTU-CVE-2026-99139

## What is CVE-2026-99139?

CVE-2026-99139 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

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

tcp: fix use-after-free in do_tcp_getsockopt(TCP_CONGESTION)

do_tcp_getsockopt() reads icsk->icsk_ca_ops->name without holding
rcu_read_lock(). Since commit 0baf26b0fcd7 ("bpf: tcp: Support
tcp_congestion_ops in bpf"), icsk_ca_ops can point to dynamically
allocated BPF struct_ops memory that may be freed concurrently via
setsockopt(TCP_CONGESTION), leading to a use-after-free.

  BUG: KASAN: slab-use-after-free in _copy_to_user+0x37/0x60
  Read of size 16 at addr ffff888013505260 by task exploit/149
   _copy_to_user+0x37/0x60
   do_tcp_getsockopt+0x158a/0x2460 (net/ipv4/tcp.c:4585)
   tcp_getsockopt+0x91/0xf0
   __sys_getsockopt+0xf7/0x170

Fix this by holding rcu_read_lock() around the ca_ops->name access,
using READ_ONCE() to load icsk_ca_ops, and copying the name to a
stack buffer before releasing the lock. Also annotate the relevant
icsk_ca_ops stores with WRITE_ONCE() to fix the accompanying KCSAN
data-race issue.

## Which versions are affected by CVE-2026-99139?


## How do I fix CVE-2026-99139?

Upgrade to a fixed version.

## Is CVE-2026-99139 being exploited?

There is no known exploitation of CVE-2026-99139 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99139 and fix it if it is affected.

What it is: CVE-2026-99139 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99139 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-2026-99139/ (Markdown: https://insights.sbomify.com/CVE-2026-99139/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99139
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99139
- OSV: https://osv.dev/vulnerability/CVE-2026-99139

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99139/
Summaries are generated and may contain mistakes; the official description above is the record.