CVE-2026-56153: Apache HTTP Server Buffer Overflow Flaw

CVE-2026-56153 Overview

CVE-2026-56153 is an out-of-bounds write vulnerability [CWE-787] in the mod_charset_lite module of Apache HTTP Server. The flaw affects Apache HTTP Server versions 2.4.0 through 2.4.68. Remote attackers can trigger the condition over the network without authentication or user interaction. The impact is limited to confidentiality, allowing exposure of sensitive memory contents from the server process.

Critical Impact
Unauthenticated remote attackers can trigger an out-of-bounds write in mod_charset_lite to disclose sensitive in-process memory from Apache HTTP Server.

Affected Products

Apache HTTP Server 2.4.0 through 2.4.68
Deployments with the mod_charset_lite module loaded
Reverse proxy and web hosting environments running vulnerable httpd builds

Discovery Timeline

2026-10-01 - CVE-2026-56153 published to NVD
2026-10-02 - Last updated in NVD database

Technical Details for CVE-2026-56153

Vulnerability Analysis

The vulnerability resides in mod_charset_lite, an Apache HTTP Server module that performs character set translation between request and response data. The module writes outside the bounds of an allocated buffer when processing specific input conditions. The resulting memory corruption leads to disclosure of adjacent memory contents rather than code execution, consistent with the confidentiality-only impact described in the advisory.

The attack is reachable over the network without credentials or user interaction. The server must have mod_charset_lite enabled and configured on a resource path accessible to the attacker. Successful exploitation can leak data from the worker process memory, including fragments of other requests, session identifiers, or configuration state.

Root Cause

The root cause is an out-of-bounds write [CWE-787] in buffer handling inside mod_charset_lite. Insufficient bounds checking during character set conversion allows the module to write past the end of a destination buffer. The Apache HTTP Server security team documents the fix in the official Apache HTTPD Vulnerabilities List.

Attack Vector

An unauthenticated remote attacker sends crafted HTTP requests to a server endpoint handled by mod_charset_lite. The module performs the faulty conversion routine and writes outside the intended buffer. The attacker observes response data or server behavior to recover leaked memory contents. No code execution path has been documented in the advisory.

No verified public exploitation code is available at the time of publication. Technical discussion appears on the OpenWall OSS-Security list.

Detection Methods for CVE-2026-56153

Indicators of Compromise

Unexpected httpd worker crashes or segmentation faults recorded in error_log
HTTP requests targeting resources configured with CharsetSourceEnc or CharsetDefault directives from unusual sources
Anomalous response bodies containing fragments of unrelated request data or memory artifacts

Detection Strategies

Inventory running Apache HTTP Server instances and flag any version in the range 2.4.0 through 2.4.68
Audit httpd.conf and included configuration files for LoadModule charset_lite_module to identify exposed instances
Correlate web access logs with worker process crash events to identify probing attempts against mod_charset_lite endpoints

Monitoring Recommendations

Forward Apache error_log and access_log data to a centralized logging platform for correlation and retention
Alert on repeated malformed requests to URIs that invoke character set translation
Monitor for abnormal httpd process restarts and memory growth that may indicate exploitation attempts

How to Mitigate CVE-2026-56153

Immediate Actions Required

Upgrade Apache HTTP Server to a version later than 2.4.68 that includes the fix referenced in the vendor advisory
If immediate patching is not possible, disable mod_charset_lite on affected servers
Restrict network exposure of affected httpd instances using firewall rules or reverse proxy allowlists
Review web application logs for evidence of probing against character set conversion endpoints

Patch Information

The Apache Software Foundation addresses CVE-2026-56153 in Apache HTTP Server releases following 2.4.68. Review the Apache HTTPD Vulnerabilities List for the fixed version number and upgrade guidance. Operators building httpd from source should rebuild against the patched release and restart all worker processes.

Workarounds

Comment out or remove the LoadModule charset_lite_module modules/mod_charset_lite.so directive and restart httpd
Remove CharsetSourceEnc, CharsetDefault, and CharsetOptions directives from virtual host and directory configurations
Place a hardened reverse proxy or web application firewall in front of vulnerable servers to filter malformed requests

bash

# Disable mod_charset_lite until the server is patched
sudo a2dismod charset_lite
sudo systemctl restart apache2

# Verify the module is no longer loaded
apachectl -M | grep -i charset