CVE-2026-56153 in HTTP Server
Summary
by MITRE • 10/01/2026
Out-of-bounds Write vulnerability in Apache HTTP Server's mod_charset_lite.
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 Apache HTTP Server, a widely deployed open-source web server software, contains an out-of-bounds write vulnerability within the mod_charset_lite module in versions ranging from 2.4.0 to 2.4.68. This specific flaw arises due to improper handling of character set conversion operations, where the application fails to adequately validate buffer boundaries before writing data. The mod_charset_lite module is designed to perform on-the-fly character encoding conversions for HTTP responses based on client preferences or server configuration directives. When processing requests that trigger these conversion routines, a logic error allows an attacker to write memory beyond the allocated limits of internal buffers used during the charset transformation process.
From a technical perspective, this vulnerability classifies as CWE-787: Out-of-bounds Write, which is particularly dangerous because it can lead to arbitrary code execution if the overwritten memory contains critical control data such as return addresses or function pointers. The root cause lies in the failure of the mod_charset_lite implementation to correctly calculate the size of the output buffer relative to the input string length after character set translation. In certain edge cases involving multi-byte characters or specific locale configurations, the calculated destination pointer advances past the end of the allocated heap memory. This allows an attacker who can control the content of HTTP responses or trigger specific charset conversion paths to corrupt adjacent memory structures.
The operational impact of this vulnerability is severe for any organization running affected versions of Apache HTTP Server without appropriate mitigations in place. An authenticated or unauthenticated remote attacker, depending on server configuration and access controls, could exploit this flaw by sending specially crafted HTTP requests that force the server into a state where charset conversion triggers the buffer overflow. Successful exploitation can result in complete system compromise, allowing the execution of arbitrary code with the privileges of the Apache process. This often leads to data theft, modification of website content, or using the compromised server as part of a botnet for further attacks against other systems on the network.
Industry standards such as MITRE ATT&CK categorize this type of vulnerability under techniques related to Initial Access and Execution via memory corruption exploits. Specifically, it aligns with Tactic TA0002: Execution and Technique T1203: Exploitation for Client Execution if client-side components are involved, or more commonly in server contexts, it facilitates lateral movement after initial compromise through privilege escalation vectors enabled by the heap corruption. The vulnerability highlights the importance of rigorous input validation and bounds checking in low-level C code that handles dynamic memory allocation during text processing tasks.
To mitigate this risk, organizations must immediately upgrade Apache HTTP Server to version 2.4.69 or later, where the issue has been resolved through improved buffer management logic within mod_charset_lite. For environments unable to patch immediately due to compatibility constraints, disabling the mod_charset_lite module via configuration directives such as UnloadModule is a viable temporary workaround if charset conversion features are not strictly required for business operations. Additionally, deploying Web Application Firewalls with rules capable of detecting anomalous memory access patterns or malformed HTTP headers may provide an additional layer of defense against exploitation attempts while patching efforts are underway. Regular security audits and static code analysis tools should be employed to identify similar buffer handling issues in other custom modules or configurations within the Apache ecosystem.