CVE-2005-3357 in HTTP Server
Summary
by MITRE
mod_ssl in Apache 2.0 up to 2.0.55, when configured with an SSL vhost with access control and a custom error 400 error page, allows remote attackers to cause a denial of service (application crash) via a non-SSL request to an SSL port, which triggers a NULL pointer dereference.
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Analysis
by VulDB Data Team • 03/12/2021
The vulnerability identified as CVE-2005-3357 represents a critical denial of service flaw within the mod_ssl module of Apache HTTP Server version 2.0 up to 2.0.55. This issue manifests when the server is configured with SSL virtual hosts that include access control mechanisms and custom error handling for HTTP 400 responses. The flaw exploits a specific interaction between SSL processing and error page rendering that leads to application instability.
The technical root cause of this vulnerability lies in a NULL pointer dereference condition that occurs during the processing of non-SSL requests sent to SSL ports. When an attacker sends a non-SSL request to a port configured for SSL with access control and custom error pages, the mod_ssl module fails to properly validate pointer references during the error handling process. This improper handling results in the application attempting to access memory at a NULL address, causing an immediate crash and termination of the Apache process.
The operational impact of this vulnerability extends beyond simple service disruption as it allows remote attackers to systematically crash Apache servers without requiring authentication or special privileges. The attack vector is particularly concerning because it can be executed against any SSL-enabled Apache server that has been configured with access control restrictions and custom error pages. This makes the vulnerability exploitable in a wide range of production environments where Apache serves SSL content with security restrictions.
From a cybersecurity perspective, this vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and demonstrates characteristics consistent with attack patterns found in the MITRE ATT&CK framework under the T1499 category for network denial of service. The flaw represents a classic example of improper input validation where the module fails to properly handle unexpected request types in SSL contexts, creating a predictable crash condition.
Mitigation strategies for this vulnerability include immediate patching of affected Apache installations to version 2.0.56 or later, which contains the necessary code fixes to properly handle non-SSL requests to SSL ports. Organizations should also consider implementing additional network-level protections such as firewall rules that restrict direct access to SSL ports from untrusted networks, and configuring Apache to use more robust error handling mechanisms that do not rely on potentially vulnerable pointer operations. Network monitoring should be enhanced to detect unusual patterns of service disruption that might indicate exploitation attempts.
The vulnerability highlights the importance of proper error handling in cryptographic modules and demonstrates how seemingly minor implementation flaws can lead to significant availability impacts. Security practitioners should ensure that all SSL configurations undergo thorough testing with various request types and that custom error pages are designed with robust input validation to prevent similar issues in other components of the web server stack. Regular security audits of web server configurations and modules should include checks for proper pointer handling and resource management to prevent similar NULL pointer dereference conditions from being introduced in future implementations.