CVE-2025-40909

CVE-2025-40909 is a medium-severity vulnerability with a CVSS 3.x base score of 5.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-426.

Key facts

• Severity: Medium (CVSS 3.x base score 5.9)
• EPSS exploit prediction: 0% (29th percentile)
• Actively exploited: Not listed in CISA KEV
• EU (EUVD) id: EUVD-2025-16506
• Weakness: CWE-426
• Published: 2025-05-30
• Last modified: 2026-06-17

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

Frequently asked questions

What is CVE-2025-40909?

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

How severe is CVE-2025-40909?

CVE-2025-40909 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability low.

Is CVE-2025-40909 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (29th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2025-40909?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2025-40909 have an EU (EUVD) identifier?

Yes. CVE-2025-40909 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-16506.

When was CVE-2025-40909 published?

CVE-2025-40909 was published on 2025-05-30 and last updated on 2026-06-17.

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
• http://www.openwall.com/lists/oss-security/2025/06/02/2
• http://www.openwall.com/lists/oss-security/2025/06/02/5
• http://www.openwall.com/lists/oss-security/2025/06/02/6
• http://www.openwall.com/lists/oss-security/2025/06/02/7
• http://www.openwall.com/lists/oss-security/2025/06/03/1
• https://lists.debian.org/debian-lts-announce/2026/04/msg00018.html

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