CVE-2025-55753
📋 TL;DR
An integer overflow in Apache HTTP Server's ACME certificate renewal process causes the backoff timer to reset to zero after approximately 30 days of consecutive renewal failures. This leads to immediate, repeated certificate renewal attempts without delays, potentially causing denial of service through resource exhaustion. The vulnerability affects Apache HTTP Server versions 2.4.30 through 2.4.65.
💻 Affected Systems
- Apache HTTP Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Continuous certificate renewal attempts consume server resources, leading to denial of service and potential service disruption for legitimate users.
Likely Case
Increased server load and resource consumption during certificate renewal failures, potentially impacting performance.
If Mitigated
Minimal impact with proper monitoring and quick certificate renewal success.
🎯 Exploit Status
Exploitation requires specific conditions: ACME certificate renewal must fail repeatedly for ~30 days. This is not a typical remote code execution or authentication bypass vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.4.66
Vendor Advisory: https://httpd.apache.org/security/vulnerabilities_24.html
Restart Required: Yes
Instructions:
1. Download Apache HTTP Server 2.4.66 from the official Apache website. 2. Stop the Apache service. 3. Backup current configuration files. 4. Install version 2.4.66. 5. Restore configuration files. 6. Start the Apache service.
🔧 Temporary Workarounds
Monitor ACME Certificate Renewals
allEnsure ACME certificate renewals succeed to prevent the 30-day failure condition from occurring.
# Check certificate renewal status regularly
# Example: Check ACME renewal logs
grep -i acme /var/log/apache2/error.log
🧯 If You Can't Patch
- Implement monitoring for ACME certificate renewal failures and address them promptly.
- Consider using alternative certificate management methods temporarily.
🔍 How to Verify
Check if Vulnerable:
Check Apache version with 'httpd -v' or 'apache2 -v'. If version is between 2.4.30 and 2.4.65 inclusive, the system is vulnerable.Check Version:
httpd -v # or apache2 -vVerify Fix Applied:
After patching, verify version is 2.4.66 or higher using 'httpd -v' or 'apache2 -v'.📡 Detection & Monitoring
Log Indicators:
- Repeated ACME certificate renewal attempts without delays
- Error logs showing certificate renewal failures
Network Indicators:
- Increased traffic to ACME certificate authorities
- Unusual patterns in certificate renewal requests
SIEM Query:
source="apache_error.log" AND "ACME" AND "renewal"