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

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

Perl versions from 5.9.4 before 5.40.4-RC1, from 5.41.0 before 5.42.2-RC1, from 5.43.0 before 5.43.9 contain a vulnerable version of Compress::Raw::Zlib. Compress::Raw::Zlib is included in the Perl package as a dual-life core module, and is vulnerable to CVE-2026-3381 due to a vendored version of zlib which has several vulnerabilities, including CVE-2026-27171. The bundled Compress::Raw::Zlib was updated to version 2.221 in Perl blead commit c75ae9cc164205e1b6d6dbd57bd2c65c8593fe94.

• https://www.cve.org/CVERecord?id=CVE-2026-3381
• https://lists.security.metacpan.org/cve-announce/msg/37638919/
• https://github.com/Perl/perl5/commit/c75ae9cc164205e1b6d6dbd57bd2c65c8593fe94
• https://metacpan.org/release/PMQS/Compress-Raw-Zlib-2.221/source/Changes
• https://metacpan.org/release/SHAY/perl-5.40.4/changes
• https://metacpan.org/release/SHAY/perl-5.42.2/changes