CVE-2020-7595 Overview
CVE-2020-7595 is a Denial of Service (DoS) vulnerability in libxml2 version 2.9.10, affecting the xmlStringLenDecodeEntities function in parser.c. The vulnerability causes an infinite loop when processing certain malformed XML input that triggers a specific end-of-file (EOF) condition. This flaw allows remote attackers to cause a denial of service by providing specially crafted XML documents that exhaust system resources.
libxml2 is a widely used XML parsing library that provides APIs for reading, writing, and manipulating XML documents. The library is used extensively across enterprise applications, Linux distributions, and embedded systems, making this vulnerability particularly impactful.
Critical Impact
Remote attackers can cause complete service unavailability by triggering an infinite loop in XML parsing, leading to CPU exhaustion and denial of service conditions across affected systems.
Affected Products
- xmlsoft libxml2 2.9.10
- Fedora 30, 31, 32
- Canonical Ubuntu Linux 12.04, 14.04, 16.04, 18.04, 19.10
- Debian Linux 9.0
- Siemens SINEMA Remote Connect Server
- NetApp Clustered Data ONTAP, SMI-S Provider, SnapDrive, SteelStore Cloud Integrated Storage
- NetApp H300S/H500S/H700S/H300E/H500E/H700E/H410S/H410C series firmware
- Oracle Real User Experience Insight, Enterprise Manager Base Platform, Enterprise Manager Ops Center
- Oracle MySQL Workbench, PeopleSoft Enterprise PeopleTools
- Oracle Communications Cloud Native Core Network Function Cloud Native Environment
Discovery Timeline
- January 21, 2020 - CVE-2020-7595 published to NVD
- December 03, 2025 - Last updated in NVD database
Technical Details for CVE-2020-7595
Vulnerability Analysis
The vulnerability exists in the xmlStringLenDecodeEntities function within the parser.c source file of libxml2. This function is responsible for decoding XML entities within strings during the parsing process. When the parser encounters a specific end-of-file condition while processing entity references, it fails to properly handle the boundary case, resulting in an infinite loop.
The vulnerability is exploitable over the network without requiring any privileges or user interaction. An attacker can craft a malicious XML document that triggers the vulnerable code path, causing the parsing thread or process to enter an infinite loop. This results in complete CPU core exhaustion for the affected process, effectively causing a denial of service condition.
The impact is limited to availability—there is no confidentiality breach or integrity violation. However, given the widespread use of libxml2 in web services, application servers, and system utilities, the potential for service disruption is significant.
Root Cause
The root cause is an improper loop termination condition (CWE-835: Loop with Unreachable Exit Condition) in the entity decoding logic. When processing XML entity references, the function enters a loop to decode embedded entities. Under certain EOF conditions, the loop's exit condition is never satisfied, causing the function to iterate indefinitely.
The fix, implemented in GNOME libxml2 commit 0e1a49c89076, adds proper boundary checks to ensure the loop terminates correctly when unexpected EOF conditions are encountered during entity processing.
Attack Vector
The attack vector is network-based and requires no authentication or user interaction:
- Delivery: Attacker sends a crafted XML document to a target application that uses libxml2 for parsing
- Trigger: The malformed XML contains entity references that trigger the EOF handling bug
- Exploitation: The parser enters an infinite loop, consuming CPU resources
- Impact: The affected service becomes unresponsive, causing denial of service
Attack scenarios include:
- Web services accepting XML input (SOAP, REST APIs with XML payloads)
- XML-RPC endpoints
- Document processing applications
- Configuration parsers that accept user-supplied XML
The vulnerability can be exploited remotely by any attacker who can submit XML content to an application using vulnerable libxml2 versions.
Detection Methods for CVE-2020-7595
Indicators of Compromise
- Sustained high CPU utilization (100% on single core) by processes using libxml2
- Processes handling XML parsing becoming unresponsive or hung
- Application logs showing XML parsing operations that never complete
- Service timeouts coinciding with receipt of XML documents from external sources
Detection Strategies
- Monitor for processes with abnormally high CPU usage that are linked to libxml2 shared libraries
- Implement application-level logging to track XML parsing duration and flag operations exceeding normal thresholds
- Deploy network-based detection for malformed XML documents targeting known vulnerable patterns
- Use software composition analysis (SCA) tools to identify systems running libxml2 version 2.9.10
Monitoring Recommendations
- Configure resource monitoring alerts for sustained 100% CPU utilization on processes handling XML
- Implement watchdog timers on XML parsing operations to detect and terminate hung processes
- Monitor application health endpoints for unresponsive services following XML processing
- Review system logs for repeated process restarts indicating DoS conditions
How to Mitigate CVE-2020-7595
Immediate Actions Required
- Upgrade libxml2 to a patched version that includes commit 0e1a49c89076
- Apply vendor-specific security patches for affected operating systems and applications
- Implement input validation to reject malformed XML documents before parsing
- Configure resource limits (CPU, memory, timeouts) for XML processing operations
Patch Information
The vulnerability has been addressed through multiple vendor patches:
- libxml2: The fix is available in GNOME libxml2 commit 0e1a49c89076
- Ubuntu: Addressed in Ubuntu Security Notice USN-4274-1
- Debian: Fixed in Debian LTS Security Announcement
- Fedora: Updates available via Fedora package announcements
- Oracle: Addressed in Oracle Critical Patch Updates
- NetApp: See NetApp Security Advisory ntap-20200702-0005
- Siemens: See Siemens Product Security Advisory SSA-292794
- CISA: Industrial control systems guidance available in CISA ICS Advisory ICSA-21-103-08
Workarounds
- Implement XML parsing timeouts to automatically terminate operations exceeding expected duration
- Use process isolation (containers, sandboxing) to limit the impact of resource exhaustion
- Deploy rate limiting on endpoints accepting XML input to reduce attack surface
- Consider using alternative XML parsing libraries with proper resource management until patches can be applied
- Implement input size limits and schema validation to reject potentially malicious XML documents
# Configuration example - Set process resource limits
# Add to /etc/security/limits.conf to limit CPU time for processes
# handling XML parsing operations
xmluser hard cpu 60
xmluser soft cpu 30
# For systemd services, add to the service unit file:
# [Service]
# CPUQuota=50%
# TimeoutSec=30
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
