CVE-2020-17525
📋 TL;DR
This vulnerability in Subversion's mod_authz_svn module causes a server crash when using in-repository authz rules with AuthzSVNReposRelativeAccessFile and a client requests a non-existent repository URL. This leads to denial of service for Subversion server users. Organizations running affected Subversion servers with specific authz configurations are impacted.
💻 Affected Systems
- Apache Subversion
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service for all Subversion users, potentially disrupting version control operations and development workflows.
Likely Case
Intermittent server crashes causing temporary service disruption until the server restarts.
If Mitigated
Minimal impact with proper monitoring and automated restart mechanisms in place.
🎯 Exploit Status
Exploitation requires sending a request to a non-existent repository URL, which is trivial to perform.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.14.1 or 1.10.7
Vendor Advisory: https://subversion.apache.org/security/CVE-2020-17525-advisory.txt
Restart Required: Yes
Instructions:
1. Upgrade Subversion to version 1.14.1 or 1.10.7. 2. Restart the Subversion server. 3. Verify the fix by checking the version.
🔧 Temporary Workarounds
Disable AuthzSVNReposRelativeAccessFile
linuxRemove or comment out the AuthzSVNReposRelativeAccessFile directive from Apache configuration.
# Edit Apache configuration file (e.g., /etc/apache2/mods-enabled/dav_svn.conf)
# Remove or comment: AuthzSVNReposRelativeAccessFile on
# Restart Apache: sudo systemctl restart apache2
🧯 If You Can't Patch
- Implement monitoring and automated restart for Subversion server processes
- Restrict network access to Subversion servers to trusted users only
🔍 How to Verify
Check if Vulnerable:
Check if AuthzSVNReposRelativeAccessFile is enabled in Apache configuration and Subversion version is below 1.14.1 or 1.10.7.Check Version:
svn --version | grep '^svn, version'Verify Fix Applied:
Confirm Subversion version is 1.14.1 or higher, or 1.10.7 or higher, and test with requests to non-existent repository URLs.📡 Detection & Monitoring
Log Indicators:
- Apache error logs showing segmentation faults or crashes in mod_authz_svn
- Subversion server process termination logs
Network Indicators:
- HTTP requests to non-existent repository paths followed by service unavailability
SIEM Query:
source="apache_error.log" AND ("segmentation fault" OR "mod_authz_svn" OR "SIGSEGV")