CVE-2023-34623 Overview
CVE-2023-34623 is a denial of service vulnerability discovered in JTidy through revision r938. The vulnerability allows attackers to cause a denial of service or potentially other unspecified impacts by supplying a crafted object that exploits cyclic dependencies within the library's processing logic. JTidy is a popular Java port of HTML Tidy, widely used for cleaning up and validating HTML markup in Java applications.
Critical Impact
Attackers can remotely crash or hang applications using vulnerable JTidy versions by submitting maliciously crafted input containing cyclic dependencies, leading to resource exhaustion and service disruption.
Affected Products
- JTidy through revision r938
- Applications and services integrating vulnerable JTidy versions
- Java-based web applications using JTidy for HTML parsing and cleanup
Discovery Timeline
- 2023-06-14 - CVE CVE-2023-34623 published to NVD
- 2025-01-03 - Last updated in NVD database
Technical Details for CVE-2023-34623
Vulnerability Analysis
This vulnerability stems from improper handling of cyclic dependencies when JTidy processes specially crafted input objects. When the library encounters data structures containing circular references, it fails to properly detect and break these cycles, leading to unbounded recursion or infinite loops. This behavior can consume excessive CPU and memory resources, ultimately causing the application to become unresponsive or crash.
The vulnerability is classified under CWE-787 (Out-of-bounds Write), though the primary observable impact is denial of service through resource exhaustion. The network-accessible nature of this vulnerability means that any application exposing JTidy functionality to untrusted input—such as web applications that clean user-submitted HTML—could be vulnerable to remote exploitation without requiring authentication.
Root Cause
The root cause of CVE-2023-34623 lies in JTidy's failure to implement proper cycle detection when traversing object graphs or processing nested structures. When presented with input containing cyclic dependencies, the parser enters an unbounded processing state, attempting to recursively resolve references that ultimately point back to previously visited nodes. This lack of depth limiting or visited-node tracking results in stack overflow conditions or infinite iteration loops.
Attack Vector
The attack vector for this vulnerability is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending a maliciously crafted HTML document or object structure to an application that processes the input using JTidy. The crafted input contains cyclic dependencies that trigger the vulnerable code path.
Exploitation scenarios include:
- Web applications that use JTidy to sanitize or format user-submitted HTML content
- Backend services that process HTML documents from external sources
- Content management systems using JTidy for HTML cleanup operations
For technical details on the vulnerability mechanism, refer to the GitHub Issue Discussion where the issue is documented.
Detection Methods for CVE-2023-34623
Indicators of Compromise
- Unusual CPU or memory spikes in applications using JTidy for HTML processing
- Application threads stuck in long-running or infinite loops during HTML parsing operations
- Out-of-memory errors or stack overflow exceptions in JTidy-related code paths
- Repeated timeout errors when processing specific HTML input documents
Detection Strategies
- Monitor application performance metrics for anomalous resource consumption during HTML processing operations
- Implement logging around JTidy parsing calls to identify inputs that cause extended processing times
- Use application performance monitoring (APM) tools to track thread states and identify hung threads in JTidy code
- Scan application dependencies using software composition analysis (SCA) tools to identify vulnerable JTidy versions
Monitoring Recommendations
- Configure alerting on memory and CPU thresholds for services that utilize JTidy
- Implement request timeout mechanisms for endpoints that process untrusted HTML input
- Enable verbose logging for JTidy operations in staging environments to identify problematic input patterns
- Regularly review dependency manifests (Maven pom.xml, Gradle build files) to track JTidy version usage
How to Mitigate CVE-2023-34623
Immediate Actions Required
- Identify all applications and services in your environment that depend on JTidy
- Review JTidy version dependencies in Maven, Gradle, or other build configurations
- Implement input size limits and processing timeouts for HTML parsing operations
- Consider alternative HTML cleaning libraries if JTidy updates are not available
Patch Information
As of the last update to this CVE, specific patch information from the JTidy project was not available in the advisory data. Organizations should monitor the JTidy GitHub repository for updates regarding fixes or patched versions. Check for newer releases that may address this vulnerability.
Workarounds
- Implement strict input validation and size limits on HTML content before passing to JTidy
- Add processing timeouts around JTidy parsing operations to prevent resource exhaustion
- Run JTidy processing in isolated threads with resource limits to contain potential DoS conditions
- Consider using alternative HTML sanitization libraries such as jsoup with proper configuration
# Example Maven dependency check command
mvn dependency:tree | grep -i jtidy
# Review output for jtidy versions and update to patched version when available
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
