CVE-2004-0751 in HTTP Server
Summary
by MITRE
The char_buffer_read function in the mod_ssl module for Apache 2.x, when using reverse proxying to an SSL server, allows remote attackers to cause a denial of service (segmentation fault).
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Analysis
by VulDB Data Team • 11/05/2024
The vulnerability identified as CVE-2004-0751 represents a critical denial of service flaw within the Apache HTTP Server's mod_ssl module version 2.x. This security issue specifically manifests when the server operates in reverse proxy mode while communicating with SSL-enabled upstream servers. The flaw resides in the char_buffer_read function implementation which fails to properly handle certain buffer operations during SSL proxy connections, creating a scenario where malicious remote attackers can trigger system instability through carefully crafted requests.
The technical root cause of this vulnerability stems from inadequate input validation and buffer management within the SSL proxy handling code path. When Apache processes requests through reverse proxy configuration to SSL servers, the char_buffer_read function receives data that it cannot properly process due to missing boundary checks and memory handling safeguards. This weakness allows attackers to send malformed or specially constructed SSL handshake data that causes the mod_ssl module to attempt invalid memory operations, resulting in segmentation faults that crash the Apache process and render the web service unavailable.
From an operational perspective, this vulnerability presents significant risk to organizations relying on Apache as their primary web server with SSL proxy functionality. The denial of service impact can be severe as it completely interrupts service availability for all clients connected to the affected Apache instance. Attackers need only send specific malformed requests to trigger the segmentation fault, making this vulnerability particularly dangerous as it requires minimal effort to exploit while delivering maximum disruption. The vulnerability affects the core SSL proxy functionality, meaning any organization using Apache with SSL reverse proxy configurations is potentially at risk.
The mitigation strategies for this vulnerability involve immediate patching of Apache installations to versions containing the fix for the mod_ssl module. Organizations should also implement network-level protections such as rate limiting and connection filtering to reduce the impact of potential attacks. Additionally, monitoring systems should be configured to detect unusual patterns of segmentation faults or process crashes that might indicate exploitation attempts. Security teams should consider implementing intrusion detection systems that can identify and block malicious requests targeting this specific vulnerability pattern.
This vulnerability aligns with CWE-125: Out-of-bounds Read and CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer, both of which are fundamental memory safety issues that have historically led to denial of service and potentially more severe exploitation vectors. From an ATT&CK framework perspective, this vulnerability maps to T1499.004: Endpoint Denial of Service and T1595.001: Network Device Software Vulnerability Analysis, representing how attackers can leverage application-level flaws to compromise system availability and potentially establish persistent access through service disruption attacks.