CVE-2024-23807: Apache Xerces-C++ Use-After-Free Bug

CVE-2024-23807 Overview

A critical use-after-free vulnerability exists in the Apache Xerces C++ XML parser affecting versions 3.0.0 through 3.2.4. The vulnerability is triggered during the scanning of external Document Type Definitions (DTDs), allowing remote attackers to potentially achieve arbitrary code execution or cause denial of service conditions.

This issue was previously disclosed as CVE-2018-1311, but that advisory incorrectly stated the fix would be available in versions 3.2.3 or 3.2.4. Users are strongly recommended to upgrade to version 3.2.5 which properly addresses this vulnerability.

Critical Impact

Remote attackers can exploit this use-after-free condition during DTD processing to execute arbitrary code, compromise system integrity, or cause application crashes, potentially affecting any system using the vulnerable XML parser.

Affected Products

• Apache Xerces-C++ versions 3.0.0 to 3.2.4

Discovery Timeline

• 2024-02-29 - CVE-2024-23807 published to NVD
• 2025-01-16 - Last updated in NVD database

Technical Details for CVE-2024-23807

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption flaw that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of Apache Xerces C++, this condition is triggered specifically during the parsing of external DTDs.

When the XML parser processes documents containing external DTD references, the parser's scanning mechanism can access memory that has already been deallocated. This creates a dangerous condition where the freed memory may have been reallocated for other purposes, leading to unpredictable behavior including potential code execution.

The vulnerability can be exploited remotely over a network connection without requiring any authentication or user interaction, making it particularly dangerous for applications that process XML content from untrusted sources.

Root Cause

The root cause stems from improper memory management within the DTD scanning functionality of the Xerces C++ parser. During the parsing of external DTD references, the parser fails to properly track the lifecycle of certain memory allocations, resulting in dangling pointer references. When these freed memory regions are subsequently accessed, the use-after-free condition occurs.

Attack Vector

The attack vector is network-based, requiring an attacker to supply a maliciously crafted XML document containing external DTD references to an application using a vulnerable version of Apache Xerces C++. The exploitation does not require authentication or any specific privileges, and can be triggered without user interaction.

An attacker would craft an XML document with a specially constructed DTD reference designed to trigger the memory deallocation and subsequent access pattern that causes the use-after-free condition. When the vulnerable parser processes this document, the memory corruption occurs, potentially allowing the attacker to control program execution or crash the application.

Detection Methods for CVE-2024-23807

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using Apache Xerces C++ during XML processing
• Anomalous memory access patterns in applications parsing XML content with external DTD references
• Suspicious XML documents containing external DTD references from untrusted or unusual sources
• Evidence of DTD fetching attempts to attacker-controlled servers

Detection Strategies

• Monitor for crashes in Xerces C++ based applications, particularly those processing external XML content
• Implement static code analysis to identify applications using vulnerable Xerces C++ versions (3.0.0 through 3.2.4)
• Deploy network monitoring to detect XML payloads containing external DTD references from untrusted sources
• Use memory debugging tools (such as AddressSanitizer or Valgrind) during testing to detect use-after-free conditions

Monitoring Recommendations

• Enable detailed logging for all XML parsing operations in affected applications
• Monitor system logs for memory-related errors or crashes in processes utilizing Xerces C++
• Implement network-level inspection for XML traffic containing DOCTYPE declarations with external entities
• Track software inventory to identify all instances of Apache Xerces C++ deployments

How to Mitigate CVE-2024-23807

Immediate Actions Required

• Upgrade Apache Xerces C++ to version 3.2.5 or later immediately
• Disable DTD processing in all applications using vulnerable versions as a temporary mitigation
• Audit all applications and systems that utilize Apache Xerces C++ for XML parsing
• Apply network-level controls to filter or inspect XML content from untrusted sources

Patch Information

Apache has released version 3.2.5 of Xerces C++ which properly fixes this use-after-free vulnerability. The fix is available through the official Apache Xerces project. Users can review the patch details in the GitHub Pull Request #54 and the Apache Mailing List announcement.

Workarounds

• Disable DTD processing via the DOM using standard parser features until patching is possible
• Set the XERCES_DISABLE_DTD environment variable when using SAX parsing
• Implement input validation to reject XML documents containing external DTD references
• Deploy applications in sandboxed environments to limit the impact of potential exploitation

# Disable DTD processing via environment variable for SAX parser
export XERCES_DISABLE_DTD=1

# For DOM parser, use the following feature settings in your application code:
# parser->setFeature(XMLUni::fgXercesLoadExternalDTD, false);
# parser->setFeature(XMLUni::fgXercesDisableDTD, true);