CVE-2025-40909

What it actually does

Race condition in Perl thread creation that temporarily alters the process-wide current working directory when cloning an open directory handle, allowing concurrent threads to observe and perform file operations against unintended paths.

Why it matters to the business

Multi-threaded Perl applications may load code or access files from unexpected locations, creating risk of data exposure, integrity issues, or unintended execution in environments running affected Perl versions.

How an attack unfolds

A local attacker crafts or influences a Perl program that opens a directory handle and spawns multiple threads; during thread creation the CWD is altered in a window visible to other threads, causing subsequent file operations such as require, open, or stat to resolve against attacker-controlled paths.

How to fix it

Upgrade perl/perl5 to the version containing commit 11a11ecf4bea72b17d250cfb43c897be1341861e or later; rebuild and restart all services using the updated interpreter.

How to confirm the fix worked

Confirm the installed Perl interpreter reports a version built after commit 11a11ecf4bea72b17d250cfb43c897be1341861e; run regression tests that exercise directory-handle thread creation under concurrent load.

Typical attack path

1. Identify or deploy a multi-threaded Perl application that opens directory handles before spawning threads
2. Time thread creation so the temporary CWD change is visible to a third thread
3. Cause the affected thread to perform a file operation that resolves to an attacker-influenced path
4. Achieve loading of malicious code or access to sensitive files

How to detect it

Review application and system logs for Perl processes performing file operations against paths that differ from expected working directories during periods of thread creation; correlate with process listings showing concurrent threads.

What your security team should do

• Prioritize patching Perl interpreters on all systems that run multi-threaded Perl code
• Inventory applications that use threads and directory handles
• Monitor for unexpected file-access patterns in Perl processes until patches are applied