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

Source: https://junglewise.ai/threats/cve-2026-55549-yamcs-reflected-xss-in-authorize-endpoint  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-28. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/org-yamcs-yamcs-core). Vendors: [Maven](https://junglewise.ai/threats/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

  ```sh
  # 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

- [https://api.github.com/users/suffs811](https://api.github.com/users/suffs811)
- [https://github.com/suffs811](https://github.com/suffs811)
- [https://api.github.com/users/suffs811/gists%7B/gist_id%7D](https://api.github.com/users/suffs811/gists%7B/gist_id%7D)
- [https://api.github.com/users/suffs811/repos](https://api.github.com/users/suffs811/repos)
- [https://avatars.githubusercontent.com/u/84633135?v=4](https://avatars.githubusercontent.com/u/84633135?v=4)
- [https://api.github.com/users/suffs811/events%7B/privacy%7D](https://api.github.com/users/suffs811/events%7B/privacy%7D)

## Related threats

- [Yamcs DOM XSS in Extension Routing](https://junglewise.ai/threats/cve-2026-55566-yamcs-dom-xss-in-extension-routing)
- [Yamcs remote code execution via unescaped StreamSQL LIKE pattern](https://junglewise.ai/threats/cve-2026-55565-yamcs-remote-code-execution-via-unescaped-streamsql-like-pattern)
- [Yamcs remote code execution via YAML injection in instance template](https://junglewise.ai/threats/cve-2026-55559-yamcs-remote-code-execution-via-yaml-injection-in-instance)
- [Yamcs unauthenticated directory traversal](https://junglewise.ai/threats/cve-2026-55552-yamcs-unauthenticated-directory-traversal)
- [Yamcs missing authorization on role and privilege enumeration endpoints](https://junglewise.ai/threats/cve-2026-55547-yamcs-missing-authorization-on-role-and-privilege-enumeration)