CVE-2026-55549: Yamcs reflected XSS in authorize endpoint

CVE-2026-55549 · Severity: medium · CVSS 6.5 · Published 2026-08-28

Yamcs is a satellite operations control system used to manage and monitor space missions. A reflected cross-site scripting vulnerability in the authorize endpoint allows attackers to inject malicious JavaScript into a user's browser via a crafted URL. This enables session hijacking—stealing access and refresh tokens to impersonate legitimate users and take over their accounts.

Technologies: org.yamcs:yamcs-core (Maven). Vendors: Maven.

Quick answers

Is CVE-2026-55549 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55549 being exploited in the wild.
How severe is CVE-2026-55549?
Medium severity, with a CVSS score of 6.5, published 28 August 2026.
Which products and versions are affected?
org.yamcs:yamcs-core (Maven) < 5.9.4, ECOSYSTEM:introduced=0,fixed=5.9.4.
Is there a fix for CVE-2026-55549?
Yes. org.yamcs:yamcs-core (Maven): upgrade to 5.9.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55549 attacked?
It is attacked over the network, in a web application.
Am I affected by CVE-2026-55549?
Check whether you run org.yamcs:yamcs-core (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • org.yamcs:yamcs-core (Maven): upgrade to 5.9.4 or later
    # set org.yamcs:yamcs-core to 5.9.4 in your pom.xml or build.gradle

Technical details

A reflected XSS vulnerability exists in Yamcs versions 5.8.6 and earlier in the OAuth2 authorize endpoint (/auth/authorize). The vulnerability resides in the authorize.html, AuthHandler.java, and HandlerContext.java components, which fail to properly sanitize user-supplied input from URL parameters (such as redirect_uri or other query parameters) before rendering them in the HTML response. An attacker can craft a malicious URL containing JavaScript payload that executes in the browser context of any logged-in user who clicks the link. This does not require user authentication by the attacker, only that a victim is logged into Yamcs. Once executed, the injected script can access HTTP-only cookies containing session tokens and exfiltrate them to an attacker-controlled server, allowing complete account takeover. The vulnerability has been patched in version 5.9.4.

Affected products

  • Yamcs yamcs-core < 5.9.4

Identifiers

  • CVE-2026-55549
  • GHSA-rxpg-wjf8-qv9c

Timeline

  • 2026-08-28: disclosed: Published to GitHub Advisory Database
  • 2026: patched: Fixed in version 5.9.4

References

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