CVE-2026-55549
MediumPublic exploitYamcs has Reflected XSS in the URL of the Authorize Endpoint
Published Aug 28, 2026 · Updated Sep 10, 2026 · Also known as GHSA-rxpg-wjf8-qv9c
Key Facts
Routine patching- CVE-2026-55549 is a medium-severity vulnerability (CVSS 6.5 v3.1) affecting org.yamcs:yamcs-core (maven), yamcs.
- It is not listed in any known-exploited vulnerabilities catalog. Public exploit code is available.
- EPSS estimates a 1.3% probability of exploitation in the next 30 days.
- Fixed versions are available, including org.yamcs:yamcs-core 5.9.4.
- Brandefense priority: routine patching, as no exploitation is known and its severity is moderate or low.
CVSS v3.1
6.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
EPSS (30-day exploit likelihood)
1.3%
Higher than 70.0% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2026-55549 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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.
Affected Products
2 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| org.yamcs:yamcs-coremaven | See advisory | 5.9.4 |
| yamcs | >= < 5.9.4 | n/a |
Patched Releases
org.yamcs:yamcs-core
5.9.4
Timeline
Publicly disclosed
Aug 28, 2026
Last updated
Sep 10, 2026
Weakness Type
- CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
References
- advisoryGHSA advisory
- advisoryhttps://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55549.json
- advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2026-55549
- articlehttps://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3
- articlehttps://github.com/yamcs/yamcs/releases/tag/yamcs-5.9.4
FAQ
Common Questions.
Yamcs is a mission control framework.
Affected: org.yamcs:yamcs-core (maven); yamcs versions >= < 5.9.4. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
Public exploit code is available.
Fixed versions are available, including org.yamcs:yamcs-core 5.9.4.
Brandefense priority: routine patching, as no exploitation is known and its severity is moderate or low.
Is CVE-2026-55549 Running On Your Attack Surface?
Brandefense maps vulnerabilities like this one to your internet-facing assets and tells you exactly where to patch.
Request A Demo