CVE-2026-55549Yamcs: Reflected XSS in the URL of the Authorize Endpoint
- 6.5MediumCVSS base score
- 1.3%Exploitation in 30 daysEPSS · top 29% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- 1Public exploitsMetasploit, Nuclei and Exploit-DB
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.
Public exploit
An exploit or proof of concept is public: anyone can try it against an unpatched system. The public collections list a Nuclei template for it. A reference of the record is tagged as an exploit. CISA's SSVC rates its exploitation: a proof of concept is public.
Show the exploits2
Nuclei templates1 template
- Yamcs <=5.8.6 - Cross-Site Scripting (Nuclei template) (opens in a new tab)
http/cves/2026/CVE-2026-55549.yamlSeverity medium
References tagged exploit1 reference
- https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c (opens in a new tab)x_refsource_CONFIRMexploit
Modules, templates and exploits as listed by the Metasploit Framework (BSD-3-Clause), ProjectDiscovery's Nuclei templates (MIT) and the Exploit Database (GPLv2), read once a day. Where the data comes from
Timeline
ID reserved
By GitHub_M
- 2 months later
· 2 months later
Published
- 4 days later
· 4 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Medium6.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N |
| NVDNVD · Awaiting Analysis | 3.1 | Medium6.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N |
- EPSS (exploitation in 30 days)
- 1.3% · top 29% of all CVEs (12 Nov 2026)
- CISA SSVC
- Exploitation: poc · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.5.
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Mavenorg.yamcs:yamcs-coreGHSA-rxpg-wjf8-qv9c (opens in a new tab)
References
References3
- https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c (opens in a new tab)x_refsource_CONFIRMexploit
- https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3 (opens in a new tab)x_refsource_MISC
- https://github.com/yamcs/yamcs/releases/tag/yamcs-5.9.4 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-67841 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-rxpg-wjf8-qv9c (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-55549)Record last updated .