CVE-2024-56171: Xmlsoft Libxml2 Use-After-Free Flaw

CVE-2024-56171 Overview

CVE-2024-56171 is a critical use-after-free vulnerability affecting libxml2, a widely-used XML parsing library. The vulnerability exists in the xmlSchemaIDCFillNodeTables and xmlSchemaBubbleIDCNodeTables functions within xmlschemas.c. Exploitation requires a crafted XML document to be validated against an XML schema containing specific identity constraints, or alternatively, a maliciously crafted XML schema must be processed by the vulnerable library.

Critical Impact

This use-after-free vulnerability can be exploited remotely without authentication, potentially allowing attackers to achieve arbitrary code execution, cause denial of service, or corrupt memory in applications that process untrusted XML content with schema validation.

Affected Products

• xmlsoft libxml2 (versions before 2.12.10 and 2.13.x before 2.13.6)
• NetApp ONTAP 9
• NetApp Active IQ Unified Manager
• NetApp HCI Compute Node
• NetApp H410C, H300S, H500S, H700S, H410S (firmware and hardware)
• NetApp Manageability Software Development Kit
• NetApp SolidFire & HCI Management Node

Discovery Timeline

• February 18, 2025 - CVE-2024-56171 published to NVD
• February 2025 - Debian LTS security announcement released
• March 28, 2025 - NetApp Security Advisory NTAP-20250328-0010 published
• November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2024-56171

Vulnerability Analysis

This use-after-free vulnerability occurs during XML Schema validation when processing identity constraints. The flaw specifically manifests in two functions within xmlschemas.c: xmlSchemaIDCFillNodeTables and xmlSchemaBubbleIDCNodeTables. These functions are responsible for managing node tables used during identity constraint validation in XML schemas.

The vulnerability can be triggered through two attack scenarios: processing a specially crafted XML document against a schema with certain identity constraints, or directly processing a malicious XML schema. Since libxml2 is a foundational library used by numerous applications and systems, the attack surface is extensive across Linux distributions, enterprise storage systems, and any application utilizing libxml2 for XML processing with schema validation enabled.

Root Cause

The root cause is improper memory management in the XML Schema validation code path. When processing identity constraints, the affected functions fail to properly track memory lifecycle, leading to a condition where freed memory can be subsequently accessed. This use-after-free condition (CWE-416) occurs because node table entries may be deallocated prematurely while still being referenced by other parts of the schema validation logic.

Attack Vector

The vulnerability is exploitable via network-based attacks where an attacker can supply malicious XML content to a vulnerable application. The attack requires no prior authentication or user interaction. An attacker would need to:

1. Identify an application using a vulnerable version of libxml2 with XML Schema validation enabled
2. Craft an XML document or schema designed to trigger the specific identity constraint processing path
3. Submit the malicious XML content to the target application for validation

The use-after-free condition could be leveraged to corrupt memory structures, potentially leading to arbitrary code execution or application crashes. For detailed technical information about this vulnerability, refer to the GNOME libxml2 Issue #828 on GitLab.

Detection Methods for CVE-2024-56171

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using libxml2 during XML Schema validation
• Memory corruption errors in application logs related to XML processing
• Anomalous XML documents containing unusual identity constraint patterns being submitted to XML processing services
• Process dumps indicating heap corruption in libxml2-related memory regions

Detection Strategies

• Implement application-level monitoring to detect crashes or abnormal terminations in services processing XML with schema validation
• Deploy memory safety tools such as AddressSanitizer (ASan) in development and testing environments to identify use-after-free conditions
• Monitor system logs for libxml2-related error messages indicating memory issues during schema validation
• Use software composition analysis (SCA) tools to inventory libxml2 versions across your environment

Monitoring Recommendations

• Enable enhanced logging for XML processing services to capture schema validation events
• Implement anomaly detection for XML input patterns that may indicate exploitation attempts
• Monitor for unusual process behavior in applications known to use libxml2 for XML Schema validation
• Track security advisories from Linux distributions and vendors for related patches

How to Mitigate CVE-2024-56171

Immediate Actions Required

• Update libxml2 to version 2.12.10 or later (for the 2.12.x branch) or version 2.13.6 or later (for the 2.13.x branch)
• Inventory all systems and applications using libxml2 to determine exposure
• Prioritize patching systems that process untrusted XML content with schema validation
• Review NetApp product deployments and apply relevant firmware updates per the NetApp Security Advisory

Patch Information

Patches are available from the libxml2 project. Organizations should update to libxml2 version 2.12.10 or 2.13.6 depending on which branch they are using. Additional security advisories have been published by Debian LTS and NetApp with distribution-specific patch guidance. The technical details of the fix can be reviewed in GNOME libxml2 Issue #828.

Workarounds

• Disable XML Schema validation for untrusted XML input where schema validation is not strictly required
• Implement input validation and sanitization to reject XML documents with suspicious identity constraint patterns before they reach libxml2
• Deploy network-level filtering to block potentially malicious XML content at the perimeter
• Consider sandboxing or containerizing applications that must process untrusted XML content

# Check installed libxml2 version
xml2-config --version

# On Debian/Ubuntu systems, check package version
dpkg -l libxml2

# On RHEL/CentOS systems, check package version
rpm -q libxml2

# Update libxml2 on Debian/Ubuntu
sudo apt update && sudo apt upgrade libxml2

# Update libxml2 on RHEL/CentOS
sudo yum update libxml2