CVE-2026-55549

Received Received - Intake

Open Redirect in Yamcs Leading to XSS

Publication date: 2026-08-28

Last updated on: 2026-08-28

Assigner: GitHub, Inc.

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.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-08-28

Last Modified

2026-08-28

Generated

2026-08-29

AI Q&A

2026-08-29

EPSS Evaluated

N/A

NVD

CVE-2026-55549

EUVD

EUVD-2026-67841

Affected Vendors & Products

Vendor	Product	Version / Range
yamcs	yamcs	to 5.9.4 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-79	The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Attack-Flow Graph

Executive Summary

This is a Reflected Cross-Site Scripting (XSS) vulnerability in Yamcs versions 5.8.6 and earlier. It occurs when the application reflects an attacker-controlled redirect_uri parameter from the GET /auth/authorize endpoint into a template without proper HTML escaping. This allows an attacker to inject malicious JavaScript code into a user's browser session.

Detection Guidance

Check Yamcs version with 'yamcs-core --version' or inspect running services. Monitor network traffic for suspicious URLs containing '/auth/authorize' with unusual parameters. Review web server logs for repeated requests to the authorize endpoint with redirect_uri values.

Impact Analysis

An attacker can craft a malicious URL that executes JavaScript when opened by a Yamcs user. The script can steal browser-held authentication tokens (access and refresh tokens) via document.cookie and send them to an attacker-controlled server. This enables account takeover if the victim clicks the link.

Mitigation Strategies

Upgrade Yamcs to version 5.9.4 or later immediately. If upgrading is not possible, restrict access to the /auth/authorize endpoint via network controls. Implement input validation for all URL parameters in the authorize endpoint. Monitor for unauthorized token exfiltration attempts.

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