What’s Vulnerable › Vulnerabilities

CVE-2025-40909: Perl threads have a working directory race condition where file operations may target unintended paths

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-05-30 · updated 2026-06-17
• Weakness: CWE-426

Description

Perl threads have a working directory race condition where file operations may target unintended paths. If a directory handle is open at thread creation, the process-wide current working directory is temporarily changed in order to clone that handle for the new thread, which is visible from any third (or more) thread already running. This may lead to unintended operations such as loading code or accessing files from unexpected locations, which a local attacker may be able to exploit. The bug was introduced in commit 11a11ecf4bea72b17d250cfb43c897be1341861e and released in Perl version 5.13.6

Affected products

• perl: from 5.13.6 before 5.41.13 — fixed in 5.41.13

How to fix

Upgrade to a fixed version: perl 5.41.13. Check the vendor advisory for mitigations.

References

• https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1098226
• https://github.com/Perl/perl5/commit/11a11ecf4bea72b17d250cfb43c897be1341861e
• https://github.com/Perl/perl5/commit/918bfff86ca8d6d4e4ec5b30994451e0bd74aba9.patch
• https://github.com/Perl/perl5/issues/10387
• https://github.com/Perl/perl5/issues/23010
• https://perldoc.perl.org/5.14.0/perl5136delta#Directory-handles-not-copied-to-threads
• https://www.openwall.com/lists/oss-security/2025/05/22/2
• http://seclists.org/fulldisclosure/2025/Sep/53
• http://seclists.org/fulldisclosure/2025/Sep/54
• http://seclists.org/fulldisclosure/2025/Sep/55
• http://www.openwall.com/lists/oss-security/2025/05/23/1
• http://www.openwall.com/lists/oss-security/2025/05/30/4

Get alerted when CVE-2025-40909 or the next vulnerability affects your stack