CVE-2026-44185: 
Apache HTTP Server vulnerability analysis and mitigation

CVE-2026-44185 is a Stack Buffer Over-Read vulnerability in Apache HTTP Server's mod_ssl module, triggered via outbound OCSP requests to an attacker-controlled OCSP server. It affects Apache HTTP Server versions 2.4.0 through 2.4.67, and was fixed in version 2.4.68 released on June 8, 2026. The vulnerability was reported on April 27, 2026, by Zhenpeng (Leo) Lin at depthfirst, and publicly disclosed on June 8, 2026. It carries a CVSS v3.1 base score of 7.3 (High) (Apache Advisory, GitHub Advisory, oss-security).

The vulnerability is classified as CWE-126 (Buffer Over-read) and resides in the send_request function within Apache's mod_ssl OCSP handling code. When Apache HTTP Server makes outbound OCSP requests to validate certificates, a malicious OCSP server can craft a response that causes the server to read beyond the bounds of a stack buffer. Exploitation requires no authentication and no user interaction — an attacker only needs to position themselves as (or control) an OCSP responder that the target Apache server queries, which can occur when OCSP stapling is enabled and the server contacts an attacker-controlled endpoint. The fix was committed to the 2.4.x branch as revision r1934919 on June 3, 2026 (oss-security, Apache Advisory).

Successful exploitation can allow an unauthenticated network attacker to read sensitive data from the Apache HTTP Server's memory (confidentiality impact), potentially modify data (integrity impact), or cause the service to crash (availability impact). The buffer over-read may expose in-memory content such as cryptographic material, session data, or other sensitive server-side information. While the individual CIA impacts are each rated Low, the combination and the unauthenticated network-accessible attack vector make this a meaningful risk for internet-facing Apache deployments with OCSP stapling enabled (GitHub Advisory, Apache Advisory).

1. Reconnaissance: Identify Apache HTTP Server instances (versions 2.4.0–2.4.67) with OCSP stapling enabled, using tools like Shodan, Censys, or direct TLS handshake inspection to observe OCSP stapling behavior.
2. Set up malicious OCSP server: Deploy a custom OCSP responder (e.g., using OpenSSL or a modified OCSP library) that returns a crafted, malformed OCSP response designed to trigger a buffer over-read in mod_ssl's send_request function.
3. Redirect OCSP traffic: Position the malicious OCSP server as the target's OCSP responder — this may be achieved via DNS poisoning, BGP hijacking, or by controlling the CA's OCSP endpoint referenced in the server's certificate.
4. Trigger the vulnerability: Wait for or force the Apache server to perform an OCSP check (e.g., during a TLS handshake with OCSP stapling), causing it to contact the malicious OCSP server and process the crafted response.
5. Achieve objective: The malformed response triggers a stack buffer over-read in mod_ssl, potentially leaking memory contents, corrupting data, or crashing the Apache process (oss-security, Apache Advisory).

• Network: Unexpected outbound OCSP requests from the Apache server to unfamiliar or newly registered IP addresses/domains; OCSP responses with anomalous sizes or malformed ASN.1 structures observed in network captures.
• Logs: Apache error logs (error_log) showing SSL/TLS errors or crashes related to OCSP processing; segmentation faults or abnormal termination of the httpd process.
• Process: Unexpected crashes or restarts of the Apache HTTP Server process (httpd), particularly during TLS handshake phases; core dump files generated in the Apache working directory.
• File System: Presence of core dump files (e.g., core, core.httpd) in the Apache installation or working directory following unexpected process termination.

Upgrade Apache HTTP Server to version 2.4.68 or later, which contains the fix committed as revision r1934919. If immediate patching is not feasible, consider disabling OCSP stapling (SSLUseStapling off) in the Apache configuration to eliminate the attack surface, or restrict outbound connections from the Apache server to only trusted, known OCSP responder IP addresses via firewall rules. Upgrading to 2.4.68 is the recommended and definitive remediation (Apache Advisory, Apache Vulnerabilities Page).

The vulnerability was covered by several cybersecurity news outlets in the context of the broader Apache HTTP Server 2.4.68 release, which addressed multiple flaws including use-after-free, DoS, XSS, and buffer overflow issues. Security community discussion was moderate, with coverage on oss-security, VulDB, and Mastodon (infosec.exchange). The Apache Software Foundation rated the severity as "low" in their advisory, which aligns with the limited exploitation potential given the attacker-controlled OCSP server precondition (oss-security, Apache Advisory).