CVE-2026-56449 in HTTP Server
Summary
by MITRE • 10/01/2026
Out-of-bounds Write vulnerability in Apache HTTP Server's mod_proxy_html with crafted HTTP response bodies.
This issue affects Apache HTTP Server: from 2.4.0 through 2.4.68.
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Analysis
by VulDB Data Team • 10/01/2026
The identified security flaw represents a critical out-of-bounds write condition located within the mod_proxy_html module of the Apache HTTP Server, specifically impacting versions ranging from 2.4.0 to 2.4.68. This vulnerability arises when the server processes specially crafted HTTP response bodies that are routed through the proxy functionality while simultaneously undergoing HTML rewriting operations. The core technical deficiency lies in the improper validation and bounds checking performed by the module during its string manipulation routines, allowing an attacker to write data beyond the allocated memory buffer boundaries.
From a technical perspective, mod_proxy_html is designed to intercept HTTP responses from backend servers and modify them before forwarding them to clients, often to adjust links or resources for correct proxying contexts. However, when processing malformed input that triggers specific edge cases in its parsing logic, the module fails to correctly calculate the destination address for memory writes. This miscalculation results in a heap-based buffer overflow where data is written into adjacent memory regions outside the intended scope of the target buffer. Such an out-of-bounds write can corrupt internal server structures, overwrite critical control data such as function pointers or object headers, and potentially lead to arbitrary code execution if the attacker can precisely control the overwritten content.
The operational impact of this vulnerability is severe due to its potential for remote exploitation without authentication in many configurations where mod_proxy_html is enabled and actively processing proxied traffic. An unauthenticated remote attacker could craft a malicious HTTP response from a compromised backend server or simulate such traffic directly if proxying rules allow it, triggering the buffer overflow condition. Successful exploitation may result in complete compromise of the underlying operating system through arbitrary code execution, denial of service via application crash due to memory corruption, or information disclosure by reading sensitive data located adjacent to the corrupted heap region. This aligns with CWE-787, which classifies out-of-bounds writes as a high-severity weakness leading to unpredictable behavior and potential security breaches.
In terms of threat modeling and attack vectors, this vulnerability maps closely to MITRE ATT&CK technique T1203, specifically the exploitation phase where vulnerabilities are leveraged for initial access or escalation. The lack of proper input validation on complex data structures processed by web server modules is a common pattern in CWE-20 Improper Input Validation flaws that have historically led to critical remote code execution incidents in major software ecosystems. The severity is further amplified because Apache HTTP Server remains one of the most widely deployed web servers globally, meaning successful exploitation could impact a significant portion of internet infrastructure if left unpatched.
Mitigation strategies must prioritize immediate patching for all affected systems running versions prior to 2.4.69. Administrators should upgrade their Apache HTTP Server installations to version 2.4.69 or later where the bounds checking logic in mod_proxy_html has been corrected. In environments where upgrading is not immediately feasible, temporary mitigations include disabling the mod_proxy_html module if it is not strictly required for business operations, thereby removing the vulnerable code path entirely. Additionally, implementing strict input validation and sanitization at the reverse proxy level or using a Web Application Firewall to inspect HTTP response bodies before they reach the Apache server can provide an additional layer of defense against crafted payloads designed to trigger this specific memory corruption flaw.