CVE-2026-6797: Sanluan PublicCMS DoS Vulnerability

CVE-2026-6797 Overview

A resource consumption vulnerability has been identified in Sanluan PublicCMS up to version 6.202506.d. The vulnerability exists in the ZipSecureFile.setMinflateRatio function within the file common/src/main/java/com/publiccms/common/tools/DocToHtmlUtils.java. This flaw allows attackers to manipulate the application in a way that leads to excessive resource consumption, potentially causing service degradation or denial of service conditions. The attack can be launched remotely, making it accessible to network-based threat actors.

Critical Impact

Remote attackers with low privileges can exploit this vulnerability to cause resource exhaustion, potentially degrading application performance or triggering denial of service conditions in PublicCMS installations.

Affected Products

• Sanluan PublicCMS up to version 6.202506.d
• PublicCMS installations using the DocToHtmlUtils component
• Applications utilizing the vulnerable ZipSecureFile.setMinflateRatio function

Discovery Timeline

• 2026-04-21 - CVE CVE-2026-6797 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6797

Vulnerability Analysis

This vulnerability (CWE-400: Uncontrolled Resource Consumption) affects the document-to-HTML conversion functionality in PublicCMS. The flaw resides in how the application handles the setMinflateRatio parameter within the ZipSecureFile processing logic. When processing specially crafted input, the application fails to properly limit resource allocation, allowing an attacker to trigger excessive memory or CPU consumption.

The vulnerability requires low-level privileges to exploit but does not require user interaction, making it relatively straightforward for authenticated attackers to abuse. The primary impact is on system availability, as successful exploitation can exhaust server resources and degrade service performance for legitimate users.

Root Cause

The root cause lies in improper resource management within the DocToHtmlUtils.java file. The ZipSecureFile.setMinflateRatio function does not adequately validate or constrain resource allocation when processing input, allowing manipulation that triggers unbounded resource consumption. This is a classic resource exhaustion vulnerability where input validation and resource limits are insufficient to prevent abuse.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker with low-level authentication can submit malicious requests that manipulate the vulnerable function. The attack does not require user interaction and can be executed directly against the affected component.

The exploitation flow typically involves:

1. Authenticating with minimal privileges to the PublicCMS application
2. Submitting crafted requests targeting the document conversion functionality
3. Triggering the ZipSecureFile.setMinflateRatio function with malicious parameters
4. Causing excessive resource consumption on the server

The vendor was contacted early about this disclosure but did not respond in any way, leaving users without an official patch at this time.

Detection Methods for CVE-2026-6797

Indicators of Compromise

• Unusual spikes in CPU or memory usage on servers running PublicCMS
• Abnormal request patterns targeting document conversion endpoints
• Excessive processing time for document-to-HTML operations
• Server performance degradation without corresponding increase in legitimate traffic

Detection Strategies

• Monitor application logs for repeated requests to document conversion functionality from the same source
• Implement rate limiting on endpoints that utilize the DocToHtmlUtils component
• Deploy application performance monitoring (APM) to detect resource consumption anomalies
• Configure alerting for unusual memory allocation patterns in Java applications

Monitoring Recommendations

• Establish baseline resource utilization metrics for PublicCMS installations
• Implement real-time monitoring of JVM heap usage and garbage collection activity
• Configure alerts for CPU utilization exceeding normal thresholds
• Monitor request rates to endpoints involving document processing functionality

How to Mitigate CVE-2026-6797

Immediate Actions Required

• Review and audit access to document conversion functionality in PublicCMS
• Implement network-level rate limiting on endpoints using the vulnerable component
• Consider disabling or restricting access to the document-to-HTML conversion feature if not required
• Monitor system resources closely for signs of exploitation attempts

Patch Information

No official patch is currently available from the vendor. According to the vulnerability disclosure, the vendor was contacted early about this issue but did not respond. Users should monitor the VulDB entry for updates on remediation options and consider implementing the workarounds below until an official fix is released.

Additional technical details can be found in the VulDB CTI Report and the submission reference.

Workarounds

• Implement request rate limiting at the web server or application firewall level
• Restrict access to document conversion endpoints to trusted users only
• Deploy resource quotas for the Java process running PublicCMS
• Consider temporarily disabling the DocToHtmlUtils functionality if not essential to operations
• Implement input validation and size limits for documents submitted for conversion

# Configuration example - Resource limits for Java application
# Add to JVM startup parameters to limit heap size
JAVA_OPTS="-Xmx512m -Xms256m -XX:MaxMetaspaceSize=256m"

# Example nginx rate limiting for document conversion endpoints
# Add to server block configuration
limit_req_zone $binary_remote_addr zone=docconvert:10m rate=5r/s;
location /api/doc/ {
    limit_req zone=docconvert burst=10 nodelay;
}