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Medium, CVSS 4.3amended

Yamcs has DOM XSS in Extension Routing

CVE-2026-55566GHSA-9272-wg2r-7xmx

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (org.yamcs:yamcs-core 5.13.2, 5.12.8), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
4.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
EPSS
  • CVE-2026-55566: 0.38% estimated exploitation activity in the next 30 days; percentile 32.08 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Attack type: Unauthenticated remote Impact: Execution of arbitrary JavaScript in a user’s browser. Affected components: extension.matcher.ts:12, extension.component.ts:40, app.component.ts:134. Yamcs is vulnerable to cross-site scripting in the /ext URL endpoint. By inputting specially crafted code into the URL, an attacker can execute arbitrary JavaScript code in a user’s browser. This URL may be sent to a user via a phishing email. <img width="940" height="294" alt="image" src="https://github.com/user-attachments/assets/d886d65c-9bb5-4599-ac11-55db83aafc0e" / Steps to Reproduce: 1. Start a Yamcs instance. 2. Insert the following URL into the browser and press enter (change ‘myproject’ to the name of your instance): 3. You will receive an alert with the number ‘1’ in it. Recommendations: 1. Use document.createElement instead of innerHTML in extension.component.ts. 2. Validate the extension against registered plugin IDs. 3. Enforce a strict custom-element-name regex before mounting.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-9272-wg2r-7xmx

  2. Revision 1 · created ·

    Published from osv record GHSA-9272-wg2r-7xmx

Agent brief

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# Patch Next advisory brief: CVE-2026-55566

Advisory: Yamcs has DOM XSS in Extension Routing
IDs: CVE-2026-55566, GHSA-9272-wg2r-7xmx
Record: https://patchnext.com/advisories/cve-2026-55566 (revision 2, source checked 26 Oct 2026, 16:56 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.yamcs:yamcs-core 5.13.2, 5.12.8. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.yamcs:yamcs-core: affected >= 5.13.0, <= 5.13.1; <= 5.12.7; fixed in 5.12.8, 5.13.2

## Suggested inspection (read-only)
- Maven org.yamcs:yamcs-core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.yamcs:yamcs-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-9272-wg2r-7xmx (OSV record GHSA-9272-wg2r-7xmx lists affected ranges: Maven org.yamcs:yamcs-core >=5.13.0 =0 <5.12.8 (fixed))
- Verified: https://github.com/advisories/GHSA-9272-wg2r-7xmx (GitHub-reviewed advisory GHSA-9272-wg2r-7xmx lists affected ranges: Maven org.yamcs:yamcs-core >=5.13.0 =0 <=5.12.7)

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