OpenClaw versions prior to 2026.3.28 implement Plivo V3 signature verification that canonicalizes query ordering for the signature but performs replay detection by hashing the raw URL. This mismatch allows an attacker to capture a valid signed webhook, reorder its query parameters, and bypass the replay cache. The result is that the same voice‑call event can be processed multiple times, potentially creating unwanted calls, incurring costs, and disrupting service availability. The flaw is a classic replay attack and is associated with CWE‑325.

The affected product is OpenClaw. All deployments running OpenClaw before version 2026.3.28 are vulnerable; no specific patch version is listed beyond the release 2026.3.28 that addresses the issue.

The CVSS score of 8.2 indicates high severity, but the EPSS score is not provided, so we cannot quantify the current likelihood of exploitation. The vulnerability is not listed in CISA KEV, meaning it has not yet been identified as a known exploited vulnerability in the field. Attackers would need to capture a valid signed webhook, a scenario that is feasible whenever Plivo V3 webhooks are exposed; the weakness can be exploited over the network by crafting a replayed request that appears legitimate because the signature still validates, but the canonicalization logic does not detect the duplicate request.