What’s Vulnerable › Vulnerabilities

CVE-2026-55549: Yamcs: Reflected XSS in the URL of the Authorize Endpoint

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-08-28 · updated 2026-09-08
• Weakness: CWE-79

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

• yamcs: before 5.9.4

References

• https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3
• https://github.com/yamcs/yamcs/releases/tag/yamcs-5.9.4
• https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c
• https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c

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