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Hermes WebUI CVE-2026-55198

HIGH
Authorization Bypass Through User-Controlled Key (CWE-639)
2026-06-17 VulnCheck
Authentication Bypass Hermes Webui
7.1
CVSS 4.0 · Vendor: VulnCheck
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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

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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
X

Lifecycle Timeline

2
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. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Obtain low-privilege Hermes WebUI account
Delivery
Identify session export endpoint
Exploit
Enumerate or guess foreign session ID
Execution
Submit authenticated export request
Persist
Receive serialized foreign session transcript
Impact
Exfiltrate cross-profile conversation data
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Vulnerability AssessmentAI

Exploitation Attacker must hold a valid authenticated session on the Hermes WebUI instance (PR:L) and must be able to reach the session export endpoint served by api/routes.py::_handle_session_export. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The vendor-supplied CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N) accurately captures the shape of the bug: remote, low-complexity, requires a valid low-privilege account, and yields high confidentiality impact with no integrity or availability impact - the 7.1 score is consistent with a multi-tenant data leak rather than a takeover primitive. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker registers or compromises any low-privilege Hermes WebUI account, then sends an authenticated request to the session export endpoint with a session identifier belonging to a different profile (obtained by guessing, enumeration, or prior knowledge). The server returns the foreign profile's serialized session transcript, allowing the attacker to exfiltrate private conversations across tenant boundaries without ever touching the victim's account.
Remediation 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). … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Inventory all Hermes WebUI deployments and confirm current version. …

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Threat intelligence, references, and detailed analysis are available after sign-in.

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CVE-2026-55198 vulnerability details – vuln.today
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