Which versions of Hermes WebUI are affected by CVE-2026-55198?

Hermes WebUI versions before 0.51.443 contain an authentication bypass that allows authenticated users to export and read session transcripts belonging to other user profiles through an insecure…. A patch is available.

How to fix or mitigate CVE-2026-55198?

Within 24 hours: Inventory all Hermes WebUI deployments and confirm current version. Within 7 days: Upgrade all instances to Hermes WebUI v0.51.443 or later. Within 30 days: Audit session export logs for unauthorized access patterns and notify affected users if cross-profile exports are detected.

Hermes WebUI CVE-2026-55198

Q: What is the CVSS score of CVE-2026-55198?

CVE-2026-55198 has a CVSS 4.0 base score of 7.1 (High). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.3%.

HIGH

Authorization Bypass Through User-Controlled Key (CWE-639)

2026-06-17 VulnCheck

Authentication Bypass Hermes Webui

7.1

CVSS 4.0 · Vendor: VulnCheck

Severity by source

Vendor (VulnCheck) PRIMARY

7.1 HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

vuln.today AI

6.5 MEDIUM

Network-reachable export endpoint, no special conditions, requires a valid low-privilege account (PR:L), no user interaction; leaks foreign session transcripts so C:H, with no integrity or availability impact.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Lifecycle Timeline

Source Code Evidence Fetched

Jun 17, 2026 - 18:49 vuln.today

Analysis Generated

Jun 17, 2026 - 18:49 vuln.today

DescriptionCVE.org

Hermes WebUI before 0.51.443 contains an authorization bypass vulnerability in the session export endpoint that allows authenticated users to access sessions from other profiles. 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.

AnalysisAI

Cross-profile session data exfiltration in Hermes WebUI before 0.51.443 lets any authenticated user retrieve session transcripts belonging to other profiles by calling the session export endpoint with a guessed or known session ID. The flaw is a classic IDOR (CWE-639) in the _handle_session_export handler, which omits active-profile ownership checks before serializing the requested session. No public exploit identified at time of analysis, but VulnCheck published a coordinated advisory and the upstream fix is shipped in v0.51.443.

Technical ContextAI

Hermes WebUI is the nesquena/hermes-webui web interface (CPE cpe:2.3:a:nesquena:hermes-webui), which organizes per-user conversation history into 'profiles' that each own a set of 'sessions'. The vulnerable code path is api/routes.py::_handle_session_export, which looks up a session purely by its identifier and returns its serialized contents without confirming that the requesting user's active profile owns that session. This is a textbook CWE-639 'Authorization Bypass Through User-Controlled Key' instance: the session ID is a user-controllable reference, and the only access control gate is authentication, not authorization on the target object.

RemediationAI

Vendor-released patch: Hermes WebUI v0.51.443, which scopes session by-id reads and exports to the active profile (upstream PRs nesquena/hermes-webui#3991 and #4269, commit 2a3baa71b81ca92da8ece8616a09f15894beec71). Operators should upgrade to 0.51.443 or later directly from the release at https://github.com/nesquena/hermes-webui/releases/tag/v0.51.443. If patching has to be deferred, restrict access to the session export endpoint at a reverse proxy (block or allowlist the export route path used by _handle_session_export), tighten account provisioning so untrusted users cannot obtain logins, and rotate or shorten session IDs to make enumeration harder - note that blocking export will also break the legitimate export feature for users, and proxy-level path filtering must track any rename of the route in future releases.