CVE-2025-39840: audit: fix out-of-bounds read in audit_compare_dname_path()

Severity: high (CVSS 7.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-09-19 · updated 2026-10-19
Weakness: CWE-125

Description

In the Linux kernel, the following vulnerability has been resolved: audit: fix out-of-bounds read in audit_compare_dname_path() When a watch on dir=/ is combined with an fsnotify event for a single-character name directly under / (e.g., creating /a), an out-of-bounds read can occur in audit_compare_dname_path(). The helper parent_len() returns 1 for "/". In audit_compare_dname_path(), when parentlen equals the full path length (1), the code sets p = path + 1 and pathlen = 1 - 1 = 0. The subsequent loop then dereferences p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read. Fix this by adding a pathlen > 0 check to the while loop condition to prevent the out-of-bounds access. [PM: subject tweak, sign-off email fixes]

Affected products

Linux kernel: from 6.14 before 6.16.6; 6.17-rc1, 6.17-rc2, 6.17-rc3, 6.17-rc4 — fixed in 6.16.6

How to fix

Upgrade to a fixed version: Linux kernel 6.16.6. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2025-39840 or the next vulnerability affects your stack