OpenClaw versions 2026.2.19 through 2026.3.30 contain an improper cache isolation flaw in the Zalo webhook replay-dedupe mechanism. When an attacker controls an authenticated Zalo webhook path in a multi‑account deployment, they can suppress legitimate events on other accounts by sending requests with matching event_name and message_id parameters. This suppression inhibits the normal flow of events, potentially disrupting notifications, workflow triggers, or other time‑sensitive actions, which constitutes a denial of service against the affected accounts.

The affected system is OpenClaw, Inc. OpenClaw. Versions older than 2026.3.31, specifically those built from 2026.2.19 up to but not including 2026.3.31, are vulnerable.

The CVSS score of 2.3 indicates a low overall severity, and there is no EPSS data or KEV listing for this vulnerability, suggesting that it is not widely exploited. The attack requires an authenticated user with access to at least one webhook target in a shared environment; the attacker must then craft webhook requests that match the event and message identifiers used by other accounts. Because the flaw is triggered by normal webhook traffic rather than an explicit exploit payload, the risk is limited to environments that employ shared authentication across multiple accounts and rely on the Zalo replay-dedupe feature.