Hermes WebUI
CVE-2026-55196
CRITICAL
Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/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
Network reachable with no auth or UI, but AC:H reflects the first-credential race window and HERMES_WEBUI_PASSKEY=1 precondition; admin takeover gives C:H/I:H while service availability is unaffected.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/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
Lifecycle Timeline
2DescriptionCVE.org
Hermes WebUI before 0.51.409 contains an authentication bypass vulnerability in passkey registration endpoints that allows unauthenticated remote attackers to register arbitrary passkeys. When HERMES_WEBUI_PASSKEY=1 is enabled with no existing credentials, POST /api/auth/passkey/register/options and POST /api/auth/passkey/register endpoints are accessible without authentication, allowing attackers to claim the first passkey and gain permanent administrative control.
AnalysisAI
Authentication bypass in Hermes WebUI before 0.51.409 allows unauthenticated remote attackers to register the first passkey on instances where HERMES_WEBUI_PASSKEY=1 is set and no credentials yet exist, yielding permanent administrative control. The flaw resides in the passkey registration API endpoints, which fail to enforce authentication during the initial enrollment window. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the target instance be running Hermes WebUI prior to 0.51.409 with the environment variable HERMES_WEBUI_PASSKEY=1 set to enable WebAuthn registration, AND that no passkey credential has yet been enrolled on the instance - the two vulnerable endpoints POST /api/auth/passkey/register/options and POST /api/auth/passkey/register only accept unauthenticated requests during this first-credential window. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector (AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N) with base score 9.1 is consistent with the description: network-reachable, low complexity, no privileges, no user interaction, with high confidentiality and integrity impact and no availability impact - reasonable since a hijacked admin account leaks and tampers with data but does not by itself crash the service. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker who can reach a freshly deployed Hermes WebUI instance that has HERMES_WEBUI_PASSKEY=1 enabled but no credentials yet sends POST /api/auth/passkey/register/options to obtain a WebAuthn challenge, then completes the ceremony with their own authenticator via POST /api/auth/passkey/register. The endpoint accepts the registration without any authentication, binding the attacker's passkey as the first administrator credential and giving them permanent admin access to subsequently log in normally. … |
| Remediation | Vendor-released patch: upgrade to Hermes WebUI v0.51.442 or later, which requires authentication for passkey enrollment (see https://github.com/nesquena/hermes-webui/releases/tag/v0.51.442 and commit 4d90577e25d5537cb07290eca3fb8abff3bab316). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all Hermes WebUI instances in your environment and determine which have passkey authentication enabled (HERMES_WEBUI_PASSKEY=1) without pre-existing credentials. …
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External POC / Exploit Code
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