CVE-2026-55198 nesquena CVE debrief

Who should care

Defenders responsible for Hermes WebUI deployments should assess exposure and prioritize upgrading to version 0.51.443 or later. This includes reviewing session export endpoint security controls and verifying exposure. Security teams should track exceptions, retest remediated assets, and close the item only after evidence is documented.

Why it matters

CVE-2026-55198 is an authorization bypass vulnerability in Hermes WebUI before 0.51.443 that allows authenticated users to access sessions from other profiles via the session export endpoint. Defenders should prioritize verifying exposure and upgrading to version 0.51.443 or later.

• Authenticated users may access sessions from other profiles.
• Session transcripts may be exfiltrated by guessing or knowing session identifiers.
• Defenders should verify exposure and upgrade to version 0.51.443 or later.

Technical summary

The _handle_session_export handler in api/routes.py fails to verify active-profile ownership before serializing session data, enabling attackers to exfiltrate foreign session transcripts by guessing or knowing session identifiers. This technical issue allows authenticated users to access sessions from other profiles via the session export endpoint in Hermes WebUI before 0.51.443. Defenders should prioritize verifying exposure and upgrading to version 0.51.443 or later. The vulnerability impacts Hermes WebUI deployments, and defenders should review session export endpoint security controls.

Defensive priority

Defenders should prioritize verifying exposure and upgrading to version 0.51.443 or later.

Recommended defensive actions

• Verify exposure by checking if the Hermes WebUI version is before 0.51.443.
• Upgrade to version 0.51.443 or later.
• Monitor for suspicious activity on the session export endpoint.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The vulnerability is caused by the _handle_session_export handler in api/routes.py failing to verify active-profile ownership before serializing session data. Evidence is limited to source-provided CVE metadata and official advisory information. Defenders should verify exposure and review session export endpoint security controls. No additional technical details are available.

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.