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

Vulnerability summary

CVE-2025-39840 is a high (CVSS 7.1) Out-of-bounds Read vulnerability in linux. EPSS estimates a 0.15% chance of exploitation in the next 30 days, higher than 4.5% of scored vulnerabilities.

Timeline

1. 19-09-2025
   PublishedVulnerability first disclosed.
2. 05-08-2026
   Last modifiedVulnerability information updated.

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]

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.