CVE-2026-0858
📋 TL;DR
This stored cross-site scripting (XSS) vulnerability in PlantUML allows attackers to inject malicious JavaScript into SVG diagrams. When applications render these compromised SVGs, arbitrary script execution occurs in the victim's browser context. Any application using vulnerable PlantUML versions to generate or display diagrams is affected.
💻 Affected Systems
- PlantUML
- Applications using PlantUML library
📦 What is this software?
Plantuml by Plantuml
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of user sessions, credential theft, and unauthorized actions performed on behalf of authenticated users when malicious diagrams are viewed.
Likely Case
Session hijacking, data exfiltration, and defacement of applications displaying user-generated PlantUML diagrams.
If Mitigated
Limited impact with proper content security policies and input validation, though XSS payloads could still execute in some contexts.
🎯 Exploit Status
Exploitation requires ability to create or modify PlantUML diagrams; no authentication needed to craft malicious payloads.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.2026.0
Vendor Advisory: https://github.com/plantuml/plantuml/releases/tag/v1.2026.0
Restart Required: Yes
Instructions:
1. Update PlantUML dependency to version 1.2026.0 or later. 2. Update pom.xml or build.gradle to use fixed version. 3. Rebuild and redeploy applications. 4. Restart any services using PlantUML.
🔧 Temporary Workarounds
Input Sanitization
allImplement server-side sanitization of PlantUML diagram content before processing
Content Security Policy
allImplement strict CSP headers to prevent script execution from SVG content
🧯 If You Can't Patch
- Disable interactive attributes in GraphViz diagram processing
- Implement output encoding for all SVG content before rendering
🔍 How to Verify
Check if Vulnerable:
Check PlantUML version in dependency files; versions below 1.2026.0 are vulnerableCheck Version:
mvn dependency:tree | grep plantuml OR gradle dependencies | grep plantumlVerify Fix Applied:
Verify PlantUML version is 1.2026.0 or higher in application dependencies📡 Detection & Monitoring
Log Indicators:
- Unusual SVG generation patterns
- Large PlantUML diagram submissions
Network Indicators:
- SVG files containing script tags or javascript: URIs
SIEM Query:
source="web_logs" AND (uri="*.svg" OR user_agent="*PlantUML*") AND (content="<script>" OR content="javascript:")