CVE-2026-24739: Symfony Path Traversal Vulnerability

CVE-2026-24739 Overview

CVE-2026-24739 is an Argument Injection vulnerability affecting the Symfony Process component, a core part of the popular PHP framework for web and console applications. The vulnerability arises from improper handling of special characters (notably =) when escaping arguments on Windows systems. When PHP is executed from an MSYS2-based environment such as Git Bash, and the Symfony Process component spawns native Windows executables, the MSYS2 argument/path conversion layer can mishandle unquoted arguments containing these characters. This can result in spawned processes receiving corrupted or truncated arguments compared to what Symfony intended.

Critical Impact

This vulnerability can lead to file operations being performed on unintended paths, potentially resulting in deletion of directory contents or entire drives when untrusted input influences process arguments through repository paths, extracted archives, temporary directories, or user-controlled configuration.

Affected Products

• Symfony versions prior to 5.4.51
• Symfony versions prior to 6.4.33
• Symfony versions 7.x prior to 7.3.11, 7.4.5
• Symfony versions 8.x prior to 8.0.5

Discovery Timeline

• 2026-01-28 - CVE CVE-2026-24739 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2026-24739

Vulnerability Analysis

This vulnerability is classified under CWE-88 (Improper Neutralization of Argument Delimiters in a Command). The core issue lies in the Symfony Process component's argument escaping mechanism on Windows platforms, which fails to properly treat certain characters as "special" when constructing command-line arguments.

When an application uses Symfony Process to invoke file-management commands (such as rmdir, del, or similar utilities) with path arguments containing the = character, the MSYS2 conversion layer may alter these arguments at runtime. This becomes particularly dangerous when:

1. The application runs within an MSYS2-based shell environment (Git Bash being the most common)
2. The Process component spawns native Windows executables
3. Untrusted input can influence the process arguments either directly or indirectly

The attack requires local access and user interaction, but the potential for high-impact integrity and availability consequences makes this a significant concern for development environments and automated tooling that rely on Symfony Process.

Root Cause

The root cause is insufficient character escaping in the Symfony Process component's Windows argument handling logic. The escaping routine did not account for how MSYS2 environments interpret certain characters differently than native Windows shells. Specifically, the = character and similar MSYS2-sensitive characters were not being quoted or escaped in a manner that would prevent MSYS2's path conversion from altering the intended argument values.

Attack Vector

The attack vector is local, requiring the attacker to influence input that flows into process arguments. Attack scenarios include:

An attacker could craft malicious input containing the = character in paths that are subsequently passed to Symfony Process commands. For example, if a Composer script or similar tooling invokes file cleanup operations using paths derived from user-controlled sources (such as package names, repository paths, or temporary directory names), the MSYS2 conversion layer could alter these paths at runtime, causing operations to target unintended filesystem locations.

The vulnerability is particularly relevant in development environments where Git Bash is commonly used, and where build tools, package managers, or deployment scripts utilize Symfony Process to execute system commands.

For detailed technical information about the vulnerability mechanism, see the GitHub Security Advisory and related GitHub Issue Discussion.

Detection Methods for CVE-2026-24739

Indicators of Compromise

• Unexpected file or directory deletions on Windows systems running PHP from MSYS2/Git Bash environments
• Process execution logs showing altered or truncated path arguments containing = characters
• Application errors indicating file operations performed on unexpected paths

Detection Strategies

• Monitor Symfony Process component invocations for path arguments containing = or other MSYS2-sensitive characters
• Implement logging to capture command-line arguments passed to spawned processes and compare intended vs actual values
• Review application code and Composer scripts for use of Symfony Process with user-controllable path inputs

Monitoring Recommendations

• Enable verbose logging for file system operations in development and CI/CD environments using Git Bash
• Set up alerts for unexpected bulk file deletions or modifications outside expected working directories
• Audit usage of Symfony Process component across projects to identify potential exposure points

How to Mitigate CVE-2026-24739

Immediate Actions Required

• Upgrade Symfony to patched versions: 5.4.51, 6.4.33, 7.3.11, 7.4.5, or 8.0.5
• Audit applications for Symfony Process usage that may accept untrusted path inputs
• Review Composer scripts and other tooling for potential exposure to this vulnerability
• Consider switching development workflows to use cmd.exe or PowerShell instead of Git Bash on Windows

Patch Information

Symfony has released patches in versions 5.4.51, 6.4.33, 7.3.11, 7.4.5, and 8.0.5 that properly escape special characters in process arguments on Windows. The fix ensures that characters like = are treated as special and appropriately quoted to prevent MSYS2 conversion layer interference.

Patch commits are available on the Symfony GitHub repository with additional changes in the secondary commit. The complete fix details can be found in the GitHub Pull Request.

Workarounds

• Avoid running PHP and related tooling from MSYS2-based shells on Windows; prefer cmd.exe or PowerShell for workflows that spawn native executables
• Avoid passing paths containing = and similar MSYS2-sensitive characters to Symfony Process when operating under Git Bash/MSYS2
• Configure MSYS2 to disable or restrict argument conversion using environment variables, understanding this may affect other tooling behavior

# Workaround: Configure MSYS2 to exclude argument conversion for specific patterns
# Add to your .bashrc or shell profile when using Git Bash
export MSYS2_ARG_CONV_EXCL="*"

# Alternative: Exclude specific executable patterns
export MSYS2_ARG_CONV_EXCL="php;composer"