---
id: "CVE-2026-99138"
kind: "vulnerability"
aliases: ["CVE-2026-99138"]
title: "Linux kernel: TCP getsockopt use-after-free with BPF congestion control"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["kernel", "linux", "runtime", "self-hosted"]
not_affected_if: ["default-config"]
published_at: "2026-10-28T11:17:33+00:00"
first_seen_at: "2026-10-28T11:32:35+00:00"
updated_at: "2026-10-28T11:36:10+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99138", "first_seen_at": "2026-10-28T11:32:35+00:00"}]
---

# Linux kernel: TCP getsockopt use-after-free with BPF congestion control

The Linux kernel's TCP TCP_CC_INFO getsockopt path reads a congestion control ops pointer without RCU protection, so a BPF struct_ops congestion control module can be freed while still in use. The sources describe a use-after-free that can be triggered by a local process calling getsockopt, which may let an attacker crash the kernel or run code.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `uname -r` and compare against the kernel version your distribution lists as fixed
- Check whether BPF struct_ops TCP congestion control modules are loaded (unknown from sources)

## Fix

- Update the Linux kernel to a release that includes the upstream commit 'tcp: fix use-after-free in do_tcp_getsockopt(TCP_CC_INFO)' (fixed versions unknown from sources)
- Reboot into the patched kernel

## Timeline

- 2026-10-28T11:32:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99138

## From the sources

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

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

do_tcp_getsockopt() reads icsk->icsk_ca_ops and dereferences the
get_info function pointer without rcu_read_lock(). With BPF struct_ops
congestion control, ca_ops can point to dynamically allocated memory
that is freed concurrently, resulting in a use-after-free when the
kernel dereferences or calls through the stale pointer.

  BUG: KASAN: slab-use-after-free in do_tcp_getsockopt+0x2037/0x23e0
  Read of size 8 at addr ffff888013701258 by task exploit/149
   do_tcp_getsockopt+0x2037/0x23e0 (net/ipv4/tcp.c:4564)
   tcp_getsockopt+0x91/0xf0
   __sys_getsockopt+0xf7/0x170

Fix this by wrapping the ca_ops load and get_info call within
rcu_read_lock()/rcu_read_unlock(), and using READ_ONCE() to load
the icsk_ca_ops pointer.

---

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