CVE-2020-24977: Libxml2 Buffer Overflow Vulnerability

CVE-2020-24977 Overview

CVE-2020-24977 is a global buffer over-read vulnerability in the GNOME project's libxml2 library version 2.9.10. The vulnerability exists in the xmlEncodeEntitiesInternal function located at libxml2/entities.c. This out-of-bounds read condition allows attackers to potentially access sensitive memory contents or cause application crashes through denial of service.

libxml2 is a widely-used XML parsing library that provides support for reading, modifying, and writing XML and HTML files. Due to its extensive adoption across Linux distributions, enterprise software, and cloud-native environments, this vulnerability has a broad impact affecting numerous downstream products and systems.

Critical Impact

Attackers can exploit this buffer over-read vulnerability to leak sensitive information from memory or trigger denial of service conditions in applications that process untrusted XML input using vulnerable versions of libxml2.

Affected Products

• xmlsoft libxml2 2.9.10
• Debian Linux 9.0
• Fedora 31, 32, 33
• openSUSE Leap 15.1, 15.2
• NetApp Active IQ Unified Manager (Windows and VMware vSphere)
• NetApp Clustered Data ONTAP
• NetApp Clustered Data ONTAP Antivirus Connector
• NetApp Inventory Collect Tool
• NetApp Manageability Software Development Kit
• NetApp SnapDrive (Unix and Windows)
• NetApp HCI H410C Firmware
• Oracle Communications Cloud Native Core Network Function Cloud Native Environment 1.10.0
• Oracle Enterprise Manager Base Platform 13.4.0.0 and 13.5.0.0
• Oracle Enterprise Manager Ops Center 12.4.0.0
• Oracle HTTP Server 12.2.1.3.0 and 12.2.1.4.0
• Oracle MySQL Workbench
• Oracle PeopleSoft Enterprise PeopleTools 8.58
• Oracle Real User Experience Insight 13.4.1.0 and 13.5.1.0

Discovery Timeline

• September 4, 2020 - CVE-2020-24977 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-24977

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read). The flaw occurs within the xmlEncodeEntitiesInternal function in libxml2/entities.c, where improper boundary checking allows read operations to access memory beyond the intended buffer limits.

When processing specially crafted XML content, the vulnerable function fails to properly validate buffer boundaries during entity encoding operations. This can lead to reading memory contents that extend past the allocated buffer, potentially exposing sensitive information stored in adjacent memory locations.

The network-accessible nature of this vulnerability means that applications parsing XML data from remote sources are at particular risk. Any application using libxml2 2.9.10 to parse untrusted XML input could be exploited to leak memory contents or experience crashes due to invalid memory access.

Root Cause

The root cause lies in insufficient bounds checking within the xmlEncodeEntitiesInternal function. During the entity encoding process, the function reads data without properly verifying that the read operations remain within the allocated buffer boundaries. This allows an attacker who can control the input XML to trigger reads beyond the buffer's end, resulting in an out-of-bounds read condition.

Attack Vector

The vulnerability can be exploited remotely over a network without requiring authentication or user interaction. An attacker can craft malicious XML input that, when processed by an application using the vulnerable libxml2 library, triggers the buffer over-read condition.

The attack scenario involves delivering specially crafted XML content to target applications. This could occur through:

• Web services that parse XML request bodies
• Document processing systems handling XML files
• APIs that accept XML-formatted data
• Applications processing XML feeds from external sources

When the malicious XML reaches the xmlEncodeEntitiesInternal function, it exploits the boundary checking flaw to read beyond allocated memory, potentially disclosing sensitive data or causing application instability.

Detection Methods for CVE-2020-24977

Indicators of Compromise

• Application crashes or segmentation faults during XML parsing operations
• Unexpected memory access patterns in processes using libxml2
• Anomalous behavior in XML processing services or applications
• Core dumps indicating out-of-bounds memory access in libxml2 components

Detection Strategies

• Monitor for application crashes in services that perform XML parsing with stack traces pointing to xmlEncodeEntitiesInternal
• Implement memory sanitizer tools (ASan, MSan) in development and testing environments to detect out-of-bounds reads
• Use static analysis tools to identify vulnerable libxml2 versions in your software inventory
• Deploy vulnerability scanning to identify systems running libxml2 2.9.10

Monitoring Recommendations

• Enable application crash reporting and logging for XML processing services
• Monitor system logs for segmentation fault signals in processes using libxml2
• Implement software composition analysis (SCA) to track libxml2 dependencies across your environment
• Set up alerts for unusual memory usage patterns in XML-processing applications

How to Mitigate CVE-2020-24977

Immediate Actions Required

• Update libxml2 to a version containing the security fix (commit 50f06b3e or later)
• Identify and inventory all applications using libxml2 2.9.10 across your environment
• Apply vendor-provided security patches for affected downstream products
• Review XML input sources and implement input validation where possible

Patch Information

The vulnerability has been fixed in libxml2 via commit 50f06b3efb638efb0abd95dc62dca05ae67882c2. Organizations should update to patched versions of libxml2 available through their distribution's package management system.

Multiple vendors have released security advisories and patches:

• GNOME libxml2 Security Commit
• GNOME libxml2 Issue Tracker
• Oracle CPU October 2021
• Oracle CPU April 2022
• NetApp Security Advisory
• Gentoo Security Advisory GLSA 202107-05

Workarounds

• Implement strict input validation on all XML data before passing to libxml2 for parsing
• Consider sandboxing XML processing operations to limit potential information disclosure
• Restrict network access for systems that must continue running vulnerable versions
• Implement Web Application Firewall (WAF) rules to filter potentially malicious XML payloads

# Check current libxml2 version
xml2-config --version

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

# Update libxml2 on RHEL/CentOS/Fedora
sudo dnf update libxml2

# Update libxml2 on openSUSE
sudo zypper update libxml2