XSS in Yamcs

CVE-2026-55566

Yamcs is a mission control framework. Prior to 5.12.8 and 5.13.2, Yamcs processes attacker-controlled data from the /ext URL route in yamcs-web/src/main/webapp/projects/webapp/src/app/core/routes/extension.matcher.ts, extension.component.ts, and app.component.ts without checking registered plugin IDs before DOM rendering through innerHTML. A crafted URL can execute JavaScript when opened by a user. The script can read data available to the Yamcs web application and perform actions in the user context. This issue is fixed in versions 5.12.8 and 5.13.2.

Vulnerability class: XSS (Cross-Site Scripting)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.004 (30.0th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 30th percentile — 30.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-55566: held from 0.003 to 0.004.

EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.001

Affected products

  • Yamcs — versions < 5.12.8, >= 5.13.0, < 5.13.2

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-55566?
CVE-2026-55566 is a medium-severity vulnerability in Yamcs, classified under Cross-site Scripting. CVSS score: 4.3/10. Published 2026-08-28.
How severe is CVE-2026-55566?
Medium severity. CVSS v3 base score is 4.3 out of 10.