CVE-2024-49960: ext4: fix timer use-after-free on failed mount

Severity: high (CVSS 7.8 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: 2024-10-21 · updated 2026-08-04
Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: ext4: fix timer use-after-free on failed mount Syzbot has found an ODEBUG bug in ext4_fill_super The del_timer_sync function cancels the s_err_report timer, which reminds about filesystem errors daily. We should guarantee the timer is no longer active before kfree(sbi). When filesystem mounting fails, the flow goes to failed_mount3, where an error occurs when ext4_stop_mmpd is called, causing a read I/O failure. This triggers the ext4_handle_error function that ultimately re-arms the timer, leaving the s_err_report timer active before kfree(sbi) is called. Fix the issue by canceling the s_err_report timer after calling ext4_stop_mmpd.

Affected products

Debian Linux: 11.0
Linux kernel: before 5.10.237; from 5.11 before 5.15.181; from 5.16 before 6.1.118; from 6.2 before 6.6.55; from 6.7 before 6.10.14; from 6.11 before 6.11.3 — fixed in 5.10.237, 5.15.181, 6.1.118, 6.10.14, 6.11.3, 6.6.55

How to fix

Upgrade to a fixed version: Linux kernel 5.10.237, 5.15.181, 6.1.118, 6.10.14. Check the vendor advisory for mitigations.

References

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