CVE-2026-0858VulnerabilityPublished 16 Jan 2026

CVE-2026-0858: net.sourceforge.plantuml:plantuml · Stored XSS

Affects net.sourceforge.plantuml:plantumlSource CVE Database V5

Not known to be exploited · CVSS 5.1 Medium : upgrade to 1.2026.0 when convenient.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 4.0 base score

5.1Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 27% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.2026.0

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: Active
Vulnerable system confidentiality: None
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: Low
Subsequent system integrity: Low
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: Active: Successful exploitation of this vulnerability requires a targeted user to perform specific, conscious interactions with the vulnerable system and the attacker’s payload, or the user’s interactions would actively subvert protection mechanisms which would lead to exploitation of the vulnerability.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the Subsequent System.
Subsequent system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Subsequent System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade net.sourceforge.plantuml:plantuml and net.sourceforge.plantuml/plantuml to 1.2026.0.

Affected software

Product	Affected	Fixed in
net.sourceforge.plantuml:plantuml	Affected <1.2026.0	Fixed in 1.2026.0
Mavennet.sourceforge.plantuml/plantuml`pkg:maven/net.sourceforge.plantuml/plantuml`Other threats	Affected <1.2026.0	Fixed in 1.2026.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should immediately upgrade PlantUML to version 1.2026.0 or later, where the vulnerability is fixed. Until upgrades are fully deployed, organizations should implement strict input validation and sanitization on any user-submitted PlantUML diagrams, especially those that generate SVG outputs. Restrict diagram submission privileges to trusted users only and avoid rendering untrusted diagrams in web contexts without proper sandboxing. Employ Content Security Policy (CSP) headers to limit the execution of inline scripts and reduce the impact of potential XSS payloads. Additionally, monitor logs and user reports for unusual behavior related to diagram rendering. Educate users about the risks of interacting with untrusted diagrams and encourage reporting of suspicious content. For web applications embedding PlantUML-generated SVGs, consider rendering diagrams server-side to static images or using safer output formats until the vulnerability is fully mitigated. Regularly review and update security policies related to third-party tools and diagram sharing platforms.

Description

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.

Impact

For European organizations, the impact of CVE-2026-0858 can be significant in environments where PlantUML is used for generating and sharing diagrams, such as software development teams, technical documentation, and collaborative platforms. Exploitation could lead to unauthorized script execution in users’ browsers, resulting in session hijacking, data leakage, or unauthorized actions within web applications that render these SVGs. This risk is heightened in organizations that allow external contributors to submit PlantUML diagrams or where diagrams are embedded in internal portals accessible by multiple users. Confidentiality could be compromised if sensitive session tokens or credentials are stolen. Integrity of user sessions and availability of services could also be indirectly affected if attackers leverage the XSS to perform further attacks such as phishing or malware delivery. Although no known exploits exist currently, the medium severity score and ease of exploitation without authentication mean that organizations should act proactively to prevent potential attacks. The vulnerability could also undermine trust in documentation and collaboration tools if exploited.

References

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