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

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-05-21 · updated 2026-06-17
Weakness: CWE-672

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.

Affected products

Linux kernel: from 4.4.173 before 4.4.277; from 4.9.155 before 4.9.277; from 4.14.98 before 4.14.241; from 4.19.20 before 4.19.199; from 5.0 before 5.4.136; from 5.5 before 5.10.54 — fixed in 4.14.241, 4.19.199, 4.4.277, 4.9.277, 5.10.54, 5.13.6

How to fix

Upgrade to a fixed version: Linux kernel 4.14.241, 4.19.199, 4.4.277, 4.9.277. Check the vendor advisory for mitigations.

References

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