CVE-2024-46901: Apache Subversion DOS Vulnerability

CVE-2024-46901 Overview

CVE-2024-46901 is an input validation vulnerability affecting Apache Subversion repositories served via mod_dav_svn. The vulnerability stems from insufficient validation of filenames against control characters, which allows authenticated users with commit access to introduce corrupted revisions into a repository. This can lead to disruption for all users accessing the affected repository.

The vulnerability specifically impacts the WebDAV-based access method (mod_dav_svn) and does not affect repositories served through other access protocols such as svnserve or local file access.

Critical Impact

Authenticated attackers with commit privileges can corrupt Subversion repositories served via mod_dav_svn, potentially disrupting version control operations for all repository users.

Affected Products

• Apache Subversion versions up to and including 1.14.4
• Debian Linux 11.0 (with vulnerable Subversion packages)
• Any system running mod_dav_svn with Apache HTTP Server

Discovery Timeline

• 2024-12-09 - CVE-2024-46901 published to NVD
• 2025-07-15 - Last updated in NVD database

Technical Details for CVE-2024-46901

Vulnerability Analysis

This vulnerability is classified as CWE-20 (Improper Input Validation). The core issue lies in how mod_dav_svn processes filename inputs during commit operations. When a user with commit access submits files containing control characters in their filenames, the module fails to properly validate and reject these malformed inputs before they are written to the repository.

The attack requires network access and authenticated privileges (commit access) to the repository. While the impact is limited to availability disruption rather than data confidentiality or integrity breaches, it can significantly impact development workflows by corrupting the repository state.

Root Cause

The root cause is insufficient input sanitization in the mod_dav_svn Apache module. The module does not adequately filter control characters (such as null bytes, carriage returns, line feeds, and other non-printable ASCII characters) from filenames before processing commits. This oversight allows specially crafted filenames to be accepted and stored, resulting in repository corruption.

Proper filename validation should reject any filename containing characters that could interfere with repository operations or violate filesystem naming conventions.

Attack Vector

The attack vector is network-based and requires authenticated access with commit privileges to the target Subversion repository. An attacker would need to:

1. Authenticate to an Apache Subversion repository served via mod_dav_svn
2. Have commit access to at least one path within the repository
3. Craft a commit containing a file with control characters embedded in the filename
4. Submit the malicious commit through the WebDAV interface

The vulnerability mechanism involves the WebDAV commit handler accepting filenames without proper sanitization. When control characters are present in filenames, subsequent operations on the repository may fail or produce unexpected behavior, effectively corrupting the revision and disrupting repository access for other users.

For detailed technical information about the vulnerability, refer to the Apache CVE-2024-46901 Advisory.

Detection Methods for CVE-2024-46901

Indicators of Compromise

• Unusual commit activity containing non-printable characters in file paths
• Repository access errors or corruption messages after recent commits
• Log entries showing malformed filenames in Apache or Subversion logs
• Users reporting inability to checkout, update, or browse specific revisions

Detection Strategies

• Monitor Apache access logs for commit operations with unusual URL-encoded characters
• Implement pre-commit hooks to validate filenames against control character patterns
• Review Subversion transaction logs for commits containing suspicious filenames
• Deploy file integrity monitoring on repository storage to detect corruption

Monitoring Recommendations

• Enable verbose logging for mod_dav_svn to capture detailed commit information
• Configure alerting for repository error conditions and access failures
• Implement automated repository health checks to detect corruption early
• Monitor user commit patterns for anomalous activity from accounts with commit access

How to Mitigate CVE-2024-46901

Immediate Actions Required

• Upgrade Apache Subversion to version 1.14.5 or later immediately
• Audit recent commits for any signs of filename manipulation or repository corruption
• Review and restrict commit access privileges to trusted users only
• Consider temporarily switching to alternative access methods (svnserve) if immediate patching is not possible

Patch Information

Apache has released version 1.14.5 of Subversion which addresses this vulnerability. Users should upgrade to this version or later to remediate the issue. Detailed patch information is available in the Apache CVE-2024-46901 Advisory.

For Debian Linux users, security updates are available through the standard package management system. Refer to the Debian LTS Announcement for distribution-specific guidance.

Workarounds

• Migrate repositories to use svnserve or SSH-based access instead of mod_dav_svn
• Implement server-side pre-commit hooks to reject filenames containing control characters
• Restrict network access to the WebDAV endpoint using firewall rules or Apache access controls
• Limit commit access to only essential personnel until patching is complete

# Example pre-commit hook to reject control characters in filenames
# Place in repository/hooks/pre-commit and make executable
#!/bin/bash
REPOS="$1"
TXN="$2"

# Check for control characters in changed paths
svnlook changed -t "$TXN" "$REPOS" | while read line; do
    if echo "$line" | grep -qP '[\\x00-\\x1F\\x7F]'; then
        echo "Error: Filename contains control characters" >&2
        exit 1
    fi
done