CVE-2022-23943: Apache HTTP Server Buffer Overflow Flaw

CVE-2022-23943 Overview

CVE-2022-23943 is an Out-of-bounds Write vulnerability in the mod_sed module of Apache HTTP Server that allows remote attackers to overwrite heap memory with potentially attacker-controlled data. This memory corruption vulnerability affects Apache HTTP Server 2.4 version 2.4.52 and prior versions, exposing web servers to serious security risks including potential remote code execution.

The vulnerability stems from improper boundary checking within the mod_sed module, which is used for stream editing of response bodies. When processing specially crafted input, the module fails to properly validate buffer boundaries, leading to heap memory corruption that could be exploited by a remote attacker over the network without any authentication or user interaction.

Critical Impact

Remote attackers can exploit this heap-based out-of-bounds write vulnerability to corrupt memory, potentially leading to arbitrary code execution, denial of service, or complete system compromise on affected Apache HTTP Server installations.

Affected Products

• Apache HTTP Server versions 2.4.52 and prior
• Fedora 34, 35, and 36
• Debian Linux 9.0
• Oracle HTTP Server 12.2.1.3.0 and 12.2.1.4.0
• Oracle ZFS Storage Appliance Kit 8.8

Discovery Timeline

• March 14, 2022 - CVE-2022-23943 published to NVD
• May 1, 2025 - Last updated in NVD database

Technical Details for CVE-2022-23943

Vulnerability Analysis

This vulnerability is classified under CWE-787 (Out-of-bounds Write) and CWE-190 (Integer Overflow or Wraparound), indicating a serious memory safety issue in the mod_sed module. The flaw allows attackers to write data beyond the allocated buffer boundaries in heap memory, which can lead to corruption of adjacent memory structures.

The mod_sed module provides sed-like stream editing functionality for Apache HTTP Server, allowing administrators to perform on-the-fly content transformations. When processing input data, the module allocates buffers for the transformation operations. However, insufficient validation of input sizes or transformation results allows attackers to trigger writes beyond these buffer boundaries.

The attack can be executed remotely over the network with no privileges or user interaction required. Successful exploitation could result in complete compromise of confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause lies in improper bounds checking within the mod_sed module's memory handling routines. Specifically, the vulnerability involves an integer overflow condition (CWE-190) that can occur during buffer size calculations, subsequently leading to an undersized buffer allocation. When data is then written to this undersized buffer, it results in an out-of-bounds write condition (CWE-787) that overwrites adjacent heap memory.

This type of vulnerability is particularly dangerous because heap memory corruption can be leveraged to overwrite critical data structures, function pointers, or metadata used by the memory allocator itself, potentially allowing attackers to gain control of program execution flow.

Attack Vector

The attack is network-based and can be executed by sending specially crafted HTTP requests to an Apache HTTP Server with the mod_sed module enabled. The attacker does not need any authentication credentials or special privileges. The attack does not require any interaction from legitimate users or administrators.

The exploitation scenario involves sending malicious input that triggers the integer overflow during buffer size calculation in mod_sed. This causes the module to allocate an insufficiently sized heap buffer, and when the actual data is written, it overflows beyond the buffer boundaries, corrupting adjacent heap memory with attacker-controlled data.

The vulnerability mechanism involves improper handling of input sizes within the mod_sed stream editing operations. When large or specially crafted transformation rules are applied to response data, an integer overflow can occur during size calculations, leading to undersized buffer allocations. Subsequent write operations then overflow these buffers, corrupting heap memory structures. For detailed technical analysis, refer to the Apache HTTP Vulnerabilities List and the OpenWall Security List Post.

Detection Methods for CVE-2022-23943

Indicators of Compromise

• Unexpected Apache HTTP Server crashes or segmentation faults, particularly when mod_sed is processing requests
• Unusual patterns in access logs showing malformed or excessively large requests targeting content transformation endpoints
• Memory corruption errors or abnormal memory usage patterns in Apache process monitoring
• Evidence of attempted exploitation in web application firewall logs showing oversized or malformed request patterns

Detection Strategies

• Deploy network-based intrusion detection systems (IDS) with signatures for detecting exploitation attempts against Apache mod_sed vulnerabilities
• Implement web application firewall (WAF) rules to detect and block abnormally large or malformed requests that could trigger buffer overflow conditions
• Use SentinelOne's real-time memory protection capabilities to detect and prevent heap-based buffer overflow exploitation attempts
• Enable Apache HTTP Server extended logging and monitor for unusual error patterns related to mod_sed processing

Monitoring Recommendations

• Monitor Apache error logs for segmentation faults, memory allocation failures, or unusual mod_sed-related error messages
• Implement real-time process monitoring for Apache httpd processes to detect abnormal memory consumption or unexpected terminations
• Configure alerting for any detected buffer overflow or memory corruption attempts through endpoint detection and response (EDR) solutions
• Regularly audit Apache HTTP Server configurations to identify systems with mod_sed enabled that may be vulnerable

How to Mitigate CVE-2022-23943

Immediate Actions Required

• Update Apache HTTP Server to version 2.4.53 or later immediately, which contains the security fix for this vulnerability
• If immediate patching is not possible, disable the mod_sed module until the update can be applied
• Review and audit all Apache HTTP Server installations across the organization to identify affected versions
• Implement network segmentation to limit exposure of vulnerable Apache servers to untrusted networks

Patch Information

Apache Software Foundation has released Apache HTTP Server version 2.4.53 which addresses this vulnerability along with other security issues. Organizations should prioritize updating to the latest stable release. Security patches are also available from various Linux distributions including Fedora and Debian.

For detailed patch information, consult the Apache HTTP Vulnerabilities List. Oracle customers should review the Oracle Critical Patch Updates for guidance on patching Oracle HTTP Server deployments. Additional vendor-specific guidance is available from NetApp Security Advisory and Tenable Security Notice TNS-2022-08.

Workarounds

• Disable the mod_sed module if stream editing functionality is not required by commenting out or removing the LoadModule directive
• Implement strict input validation at the network perimeter using a web application firewall to filter potentially malicious requests
• Restrict access to the Apache HTTP Server to trusted networks only while awaiting patch deployment
• Consider deploying a reverse proxy in front of vulnerable Apache instances to provide an additional layer of request filtering

# Disable mod_sed in Apache configuration
# Edit httpd.conf or apache2.conf and comment out or remove:
# LoadModule sed_module modules/mod_sed.so

# Alternatively, use a2dismod on Debian/Ubuntu systems:
sudo a2dismod sed
sudo systemctl restart apache2

# Verify mod_sed is disabled:
apachectl -M | grep sed