Apache HTTP Server HTTP/2 Protocol Vulnerability Could Allow for Remote Code Execution

A vulnerability has been identified in Apache HTTP Server related to the HTTP/2 protocol. This flaw allows a remote attacker to potentially cause a denial-of-service condition by crashing worker processes. While the default configuration typically results in a denial of service, certain setups that utilize APR with mmap, which are commonly found on Debian systems and official Docker images, are susceptible to remote code execution. This is a critical vulnerability for organizations utilizing Apache HTTP Server, especially those with Debian-based systems or Docker deployments, as successful exploitation could lead to significant service disruption or complete system compromise.

Attack Chain

1. The attacker sends a specially crafted HTTP/2 request to the target Apache HTTP Server.
2. The HTTP/2 protocol handling within Apache HTTP Server improperly processes the malicious request.
3. If the server is configured with APR and mmap (commonly on Debian and Docker images), the vulnerability can be leveraged for RCE.
4. The mmap function allocates memory regions without proper validation due to the flaw in the HTTP/2 protocol handling.
5. The attacker is able to inject malicious code into the server’s memory space.
6. The injected code is then executed by the worker process.
7. The attacker gains control over the worker process, allowing them to execute arbitrary commands.
8. The attacker can then use the compromised worker process to move laterally within the network, exfiltrate data, or cause further damage.

Impact

Successful exploitation of this vulnerability could result in a denial of service for all websites hosted on the affected Apache HTTP Server by crashing worker processes with minimal effort. In specific configurations (APR with mmap, common on Debian systems and official Docker images), remote code execution is possible, potentially leading to complete server compromise, data breaches, and further lateral movement within the network. The number of potentially affected servers is substantial, given the widespread use of Apache HTTP Server.

Recommendation

• Apply the latest security patches to Apache HTTP Server to remediate the vulnerability as soon as they are available from the vendor.
• Monitor web server logs for suspicious HTTP/2 requests that may indicate exploitation attempts. Deploy the Sigma rule Detect Malicious HTTP2 Requests to identify such activity.
• For Debian systems and Docker images using APR with mmap, review configurations and consider disabling mmap where possible to mitigate the risk of RCE.
• Enable Sysmon process creation logging to activate the rule Detect Apache Process Spawning Shell to catch unexpected shell execution from the Apache process.