Yamcs: DOM XSS in Extension Routing

Answer in brief

CVE-2026-55566 records a Medium severity (CVSS 4.3) vulnerability in Yamcs: DOM XSS in Extension Routing. The current sources do not mark it as known exploited. The current feed maps org.yamcs:yamcs-core (maven), org.yamcs:yamcs-core (maven). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 28, 2026Updated Aug 28, 2026Source checked Aug 28, 2026First seen by HOL Aug 28, 2026Material review Aug 28, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 4.3
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 4.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps org.yamcs:yamcs-core (maven), org.yamcs:yamcs-core (maven). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
org.yamcs:yamcs-coremaven	>=5.13.0,<=5.13.1	5.13.2
org.yamcs:yamcs-coremaven	<=5.12.7	5.12.8

Recommended response

Check inventory. Check lockfiles and deployed manifests for org.yamcs:yamcs-core, org.yamcs:yamcs-core.
Review the reported fix. Update org.yamcs:yamcs-core to 5.13.2; org.yamcs:yamcs-core to 5.12.8 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 28, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 28, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 28, 2026

Sources and claim methodology

Upstream source description

Yamcs is a mission control framework. Prior to 5.12.8 and 5.13.2, Yamcs processes attacker-controlled data from the /ext URL route in yamcs-web/src/main/webapp/projects/webapp/src/app/core/routes/extension.matcher.ts, extension.component.ts, and app.component.ts without checking registered plugin IDs before DOM rendering through innerHTML. A crafted URL can execute JavaScript when opened by a user. The script can read data available to the Yamcs web application and perform actions in the user context. This issue is fixed in versions 5.12.8 and 5.13.2.

Quoted source text, attributed separately from HOL analysis.