CVE-2026-55549 Yamcs: Reflected XSS in the URL of the Authorize Endpoint
Attackers can execute JavaScript via a crafted authorization URL, potentially stealing authentication tokens and compromising user accounts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-55549?
CVE-2026-55549 is a medium-severity cross-site scripting vulnerability in yamcs, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2026-55549?
2 open source packages ship an affected version, including org.yamcs:yamcs-core.
| Package | Affected | Fixed in |
|---|---|---|
org.yamcs:yamcs-core Maven | All versions | 5.9.4 |
org.yamcs:yamcs-core Maven | All versions | 5.9.4 |
How do I fix CVE-2026-55549?
Upgrade org.yamcs:yamcs-core to 5.9.4 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-55549 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55549 exists.
Public exploit code: 1 Nuclei template.
Sources
Also known as GHSA-rxpg-wjf8-qv9c.