CVE-2025-23048
📋 TL;DR
This CVE describes an access control bypass vulnerability in Apache HTTP Server's mod_ssl module when using TLS 1.3 session resumption. Organizations running Apache 2.4.35-2.4.63 with multiple virtual hosts using different client certificate authentication configurations are affected. The vulnerability allows clients trusted for one virtual host to potentially access other virtual hosts.
💻 Affected Systems
- Apache HTTP Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Unauthorized access to sensitive data or systems protected by client certificate authentication, potentially leading to data breaches or privilege escalation.
Likely Case
Access to internal applications or APIs that should be restricted to specific client certificates, potentially exposing sensitive information.
If Mitigated
Limited impact if SSLStrictSNIVHostCheck is enabled or if single virtual host configurations are used.
🎯 Exploit Status
Exploitation requires a client certificate trusted by at least one virtual host and TLS 1.3 session resumption capabilities.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Apache HTTP Server 2.4.64 or later
Vendor Advisory: https://httpd.apache.org/security/vulnerabilities_24.html
Restart Required: Yes
Instructions:
1. Download Apache HTTP Server 2.4.64 or later from official sources. 2. Backup current configuration. 3. Install the updated version following Apache's installation guide. 4. Restart Apache service.
🔧 Temporary Workarounds
Enable SSLStrictSNIVHostCheck
allEnables strict Server Name Indication (SNI) host checking which prevents the bypass
SSLStrictSNIVHostCheck on
Disable TLS 1.3 session resumption
allPrevents exploitation by disabling the vulnerable TLS 1.3 feature
SSLProtocol -all +TLSv1.2
🧯 If You Can't Patch
- Enable SSLStrictSNIVHostCheck in all virtual host configurations
- Consider consolidating virtual hosts or using single client certificate authority for all hosts
🔍 How to Verify
Check if Vulnerable:
Check Apache version with 'httpd -v' and verify configuration has multiple virtual hosts with different SSLCACertificateFile/Path settings and SSLStrictSNIVHostCheck disabled.Check Version:
httpd -vVerify Fix Applied:
Verify Apache version is 2.4.64+ with 'httpd -v' and confirm SSLStrictSNIVHostCheck is enabled in configurations.📡 Detection & Monitoring
Log Indicators:
- Unexpected access patterns between virtual hosts
- TLS 1.3 session resumption logs showing cross-host access
Network Indicators:
- TLS 1.3 handshakes followed by cross-virtual-host requests
SIEM Query:
source="apache_access" (virtual_host_A AND client_cert_B) OR (virtual_host_B AND client_cert_A) where A and B are different virtual hosts