OpenClaw versions older than 2026.8.1 impose an SMS webhook invalid‑request rate limit before verifying the Twilio signature and use only the raw proxy socket address to identify clients. The vulnerability allows an unauthenticated sender to exhaust the shared pre‑authentication rate‑limit budget with invalid requests, resulting in legitimate, correctly signed Twilio callbacks returning HTTP 429 responses. The attacker cannot forge a callback or read the message data; however, legitimate SMS traffic is temporarily dropped until the shared limit window is reset.

The affected product is the OpenClaw npm package, with versions starting at 2026.6.6 up to but not including 2026.8.1. Deployments where the SMS/Twilio webhook sits behind a trusted reverse proxy or tunnel, causing multiple external clients to share one socket address, are vulnerable.

The CVSS score of 6.9 indicates a moderate severity. Exploitability appears straightforward if a deployment uses the described proxy configuration, though proof of exploitation is not publicly documented. EPSS is not available, and the vulnerability is not listed in CISA's KEV catalog. The likely attack vector is a remote unauthenticated sender sending malformed SMS webhook requests to the shared endpoint, reinforcing the rate limit and denying service to valid messages.