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

CVE-2026-99139 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99139, released November 3, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-99139
- Priority: High
- CVSS: 7.8 (Important)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 28, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99139

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99139](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99139.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.13-1 | [DEBIAN-CVE-2026-99139](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99139.md) | Nov 3, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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