Executive brief
NousResearch hermes-agent is a library used for building AI agents and handling integrations. A flaw in its Feishu webhook handler allows unauthenticated remote attackers to trigger a denial-of-service condition. By sending a flood of invalid requests, an attacker can exhaust the system's rate limits, causing legitimate messages and automated workflows to be blocked or dropped.
Technical details
An uncontrolled resource consumption vulnerability (CWE-400) exists in the `_handle_webhook_request` function within `gateway/platforms/feishu.py` of the NousResearch hermes-agent. The root cause is a logic flaw where rate limiting is applied to incoming Feishu webhook requests before the system validates the request's verification token or cryptographic signature. A remote, unauthenticated attacker can exploit this by sending a high volume of malformed or unsigned requests. Because these invalid requests increment the shared rate-limit bucket, legitimate traffic from the same source (or sharing the same rate-limit key) will be rejected with HTTP 429 (Too Many Requests) errors. As of the advisory date, no official patch has been released by the vendor.
Affected products
- NousResearch hermes-agent <= 0.19.0
Timeline
- 2026-05-07: disclosed: Initial researcher disclosure via GitHub Gist
- 2026-06-01: advisory: Published to GitHub Advisory Database and NVD