5.1

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-0858

CVE-2026-0858: PlantUML is vulnerable to Stored XSS due to insufficient sanitization of interactive attributes in GraphViz diagrams

Versions of the package net.sourceforge.plantuml:plantuml before 1.2026.0 are vulnerable to Stored XSS due to insufficient sanitization of interactive attributes in GraphViz diagrams. As a result, a crafted PlantUML diagram can inject malicious JavaScript into generated SVG output, leading to arbitrary script execution in the context of applications that render the SVG.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2026-0858

CVE-2026-0858:

5.1

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
net.sourceforge.plantuml:plantuml	maven	< 1.2026.0	1.2026.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability is a stored Cross-Site Scripting (XSS) issue in PlantUML's handling of Graphviz diagrams. The root cause is insufficient sanitization of attributes within the diagram's data before it is rendered into an SVG file. The patch addresses the vulnerability by completely removing the sanitization logic and disabling SVG export for the PSystemDot class, which handles these diagrams. The analysis of the patch identified the key functions involved in the vulnerable process. The exportDiagramNow function was the entry point that took the user-provided diagram data. It called the filter function, which in turn used sanitizeDotAttribute and sanitizeAttributeValue to try to clean the data. However, this cleaning process was flawed, allowing an attacker to craft a diagram with malicious JavaScript in attributes like URL, href, or tooltip. When the application rendered the SVG, this script would be executed in the user's browser. The removal of this entire sanitization chain and the disabling of the feature are strong indicators that these functions were central to the vulnerability.

Vulnerable functions

net.sourceforge.plantuml.directdot.PSystemDot.exportDiagramNow

src/main/java/net/sourceforge/plantuml/directdot/PSystemDot.java

This function was responsible for exporting the diagram. It previously called the `filter` function to sanitize the input data before passing it to Graphviz for SVG generation. The sanitization was insufficient, making this function the entry point for the vulnerability.

net.sourceforge.plantuml.directdot.PSystemDot.filter

src/main/java/net/sourceforge/plantuml/directdot/PSystemDot.java

This function, which was completely removed in the patch, contained the insufficient sanitization logic. It attempted to remove 'javascript:' URIs and script tags, and called helper functions to sanitize attributes, but these measures could be bypassed.

net.sourceforge.plantuml.directdot.PSystemDot.sanitizeDotAttribute

src/main/java/net/sourceforge/plantuml/directdot/PSystemDot.java

This helper function, removed in the patch, was used by `filter` to find and sanitize specific attributes in the Graphviz data. Its logic was part of the vulnerable sanitization process.

net.sourceforge.plantuml.directdot.PSystemDot.sanitizeAttributeValue

src/main/java/net/sourceforge/plantuml/directdot/PSystemDot.java

This function, also removed, performed the final step of sanitization by attempting to remove characters and patterns commonly used in XSS attacks, such as angle brackets and 'on...' event handlers. This sanitization was incomplete and could be bypassed.

Vulnerability Intelligence
Miggo AI

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WAF Protection Rules

WAF Rule

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Reasoning

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