Yamcs: Reflected XSS in the URL of the Authorize Endpoint (CVE-2026-55549) | HOL Guard CVE

Medium · CVSS 6.5CVE-2026-55549GHSA-RXPG-WJF8-QV9C

Yamcs: Reflected XSS in the URL of the Authorize Endpoint

Answer in brief

CVE-2026-55549 records a Medium severity (CVSS 6.5) vulnerability in Yamcs: Reflected XSS in the URL of the Authorize Endpoint. The current sources do not mark it as known exploited. The current feed maps 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 6.5
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 6.5. 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). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
org.yamcs:yamcs-coremaven	<5.9.4	5.9.4

Recommended response

Check inventory. Check lockfiles and deployed manifests for org.yamcs:yamcs-core.
Review the reported fix. Update org.yamcs:yamcs-core to 5.9.4 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 5.9.4, Yamcs reflects an attacker-controlled redirect_uri parameter from GET /auth/authorize into yamcs-core/src/main/resources/auth/templates/authorize.html without adequate HTML escaping by yamcs-core/src/main/java/org/yamcs/http/auth/AuthHandler.java and yamcs-core/src/main/java/org/yamcs/http/HandlerContext.java. A crafted authorization URL can execute JavaScript when opened by a Yamcs user. The script can access browser-held authentication material and transmit it to an attacker, enabling account compromise. This issue is fixed in version 5.9.4.

Quoted source text, attributed separately from HOL analysis.