CVE-2021-47356: mISDN: fix possible use-after-free in HFC_cleanup()

Severity: high (CVSS 7.7 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-416

Description

In the Linux kernel, the following vulnerability has been resolved: mISDN: fix possible use-after-free in HFC_cleanup() This module's remove path calls del_timer(). However, that function does not wait until the timer handler finishes. This means that the timer handler may still be running after the driver's remove function has finished, which would result in a use-after-free. Fix by calling del_timer_sync(), which makes sure the timer handler has finished, and unable to re-schedule itself.

Affected products

Linux kernel: before 4.4.276; from 4.5 before 4.9.276; from 4.10 before 4.14.240; from 4.15 before 4.19.198; from 4.20 before 5.4.133; from 5.5 before 5.10.51 — fixed in 4.14.240, 4.19.198, 4.4.276, 4.9.276, 5.10.51, 5.12.18

How to fix

Upgrade to a fixed version: Linux kernel 4.14.240, 4.19.198, 4.4.276, 4.9.276. Check the vendor advisory for mitigations.

References

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