CVE-2026-55549 yamcs CVE debrief

Who should care

Defenders responsible for systems using Yamcs, especially those in mission control or critical infrastructure, should assess exposure and prioritize verification and remediation efforts.

Why it matters

CVE-2026-55549 is a medium-severity vulnerability in Yamcs that allows JavaScript execution via crafted authorization URLs, potentially leading to account compromise and disruption of mission control operations. Defenders should prioritize verifying exposure, especially for systems using Yamcs versions prior to 5.9.4, and implement compensating controls to detect and prevent exploitation.

• Potential for account compromise through authentication material theft
• Possible disruption of mission control operations through JavaScript execution
• Need for verification of affected versions and exposure
• Priority for updating to version 5.9.4 or later

Technical summary

CVE-2026-55549 is a vulnerability in Yamcs, a mission control framework, that allows JavaScript execution via a crafted authorization URL. The vulnerability exists in versions prior to 5.9.4 and is fixed in version 5.9.4. This medium-severity vulnerability can lead to account compromise and disruption of mission control operations. Defenders should prioritize verifying exposure and assessing the impact of this vulnerability on their systems, especially those using Yamcs versions prior to 5.9.4. The vulnerability can be mitigated by updating to version 5.9.4 or later.

Defensive priority

Defenders should prioritize verifying exposure and assessing the impact of this vulnerability on their systems, especially those using Yamcs versions prior to 5.9.4.

Recommended defensive actions

• Verify if the system uses Yamcs versions prior to 5.9.4 and assess exposure
• Implement compensating controls to detect and prevent exploitation
• Monitor for suspicious activity related to authentication and authorization
• Update to version 5.9.4 or later if vulnerable
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but the scope of affected systems and versions requires further verification. The CVE record was published on 2026-08-28T20:18:28.657Z and has not been modified since then. The vulnerability allows JavaScript execution via a crafted authorization URL, potentially leading to account compromise. Defenders should verify exposure, especially for systems using Yamcs versions prior to 5.9.4, and implement compensating controls to detect and prevent exploitation.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.