CVE-2026-49956: Hermes WebUI Profile Isolation Bypass – Unauthenticated Session Data Disclosure

Technical summary

CVE-2026-49956 is an authorization bypass affecting Hermes WebUI's session search handler. The vulnerability stems from insufficient access control on the sessions search endpoint (CWE-862: Missing Authorization). Authenticated users can craft requests that lack active-profile filtering, allowing the endpoint to return session data across multiple profiles instead of restricting results to the attacker's own profile. The flaw permits disclosure of session metadata and message content from arbitrary profiles within the same Hermes instance.

Business impact

Multi-tenant or shared Hermes WebUI deployments face significant data exposure risk. User conversations, transcripts, and session information can be harvested by any authenticated account, potentially revealing sensitive business discussions, personal information, or confidential strategies discussed within the platform. This violates data confidentiality expectations and may trigger compliance violations depending on the nature of data stored in Hermes instances and applicable regulations.

Affected systems

Hermes WebUI versions before 0.51.269 are affected. Organizations running Hermes should check their deployed version immediately. The vulnerability affects all instances unless patched or upgraded to 0.51.269 or later.

Exploitability

This vulnerability has a CVSS 3.1 score of 6.5 (Medium) with a network attack vector, low complexity, and no user interaction required. Exploitation requires valid authentication credentials but is otherwise straightforward—an attacker need only send a malformed or unfiltered session search request. The barrier to weaponization is low for any insider or account holder with legitimate access to a Hermes instance.

Remediation

Upgrade Hermes WebUI to version 0.51.269 or later. The patch restores proper profile isolation by enforcing active-profile filtering on the session search endpoint. Organizations should prioritize patching based on the sensitivity of data stored in their Hermes instances and the number of user accounts with access.

Patch guidance

Apply Hermes WebUI version 0.51.269 or any subsequent release. Verify compatibility with your deployment before rolling out in production. Monitor upgrade changelogs for any behavioral changes to session search functionality. Test in a staging environment to confirm that profile isolation is properly enforced post-patch.

Detection guidance

Monitor for anomalous session search requests, particularly those lacking profile context or containing requests for sessions not assigned to the authenticated user. Review access logs for the sessions search handler to identify accounts querying data outside their assigned profiles. Implement alerting on cross-profile session queries if your logging and SIEM infrastructure can distinguish profile boundaries in Hermes request logs.

Why prioritize this

While the CVSS score is Medium, the risk should be elevated in environments where Hermes stores sensitive data, personal information, or business-critical conversations. The low complexity of exploitation and the requirement for only basic authentication make this a practical attack for insiders or compromised accounts. Organizations with stringent data governance or compliance requirements should treat this as higher priority.

Risk score, explained

The CVSS 3.1 score of 6.5 reflects a network-accessible endpoint (AV:N), straightforward exploitation technique (AC:L), mandatory authentication (PR:L), confidentiality impact (C:H), and no integrity or availability impact. The Medium severity appropriately captures that data disclosure is serious but does not affect service availability or allow modification of records. Context-specific factors—such as the sensitivity of stored conversations and number of users—may justify treating this as higher priority than the base score alone suggests.

Frequently asked questions