CVE-2026-31449: ext4: validate p_idx bounds in ext4_ext_correct_indexes

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-22 · updated 2026-10-19
Weakness: CWE-125

Description

In the Linux kernel, the following vulnerability has been resolved: ext4: validate p_idx bounds in ext4_ext_correct_indexes ext4_ext_correct_indexes() walks up the extent tree correcting index entries when the first extent in a leaf is modified. Before accessing path[k].p_idx->ei_block, there is no validation that p_idx falls within the valid range of index entries for that level. If the on-disk extent header contains a corrupted or crafted eh_entries value, p_idx can point past the end of the allocated buffer, causing a slab-out-of-bounds read. Fix this by validating path[k].p_idx against EXT_LAST_INDEX() at both access sites: before the while loop and inside it. Return -EFSCORRUPTED if the index pointer is out of range, consistent with how other bounds violations are handled in the ext4 extent tree code.

Affected products

Linux kernel: from 2.6.19.1 before 6.12.80; from 6.13 before 6.18.21; from 6.19 before 6.19.11; 2.6.19, 2.6.19-rc2, 2.6.19-rc3, 2.6.19-rc4, 2.6.19-rc5, 2.6.19-rc6 (+5) — fixed in 6.12.80, 6.18.21, 6.19.11

How to fix

Upgrade to a fixed version: Linux kernel 6.12.80, 6.18.21, 6.19.11. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-31449 or the next vulnerability affects your stack