CVE-2026-42437: 
OpenClaw (formerly Moltbot or Clawdbot) vulnerability analysis and mitigation

CVE-2026-42437 is a denial-of-service vulnerability in OpenClaw affecting versions >= 2026.4.9 and < 2026.4.10 (npm package). The vulnerability exists in the voice-call realtime WebSocket path, which accepts oversized frames without proper size validation, allowing remote unauthenticated attackers to cause service unavailability. It was published on May 5, 2026, and assigned a CVSS v3.1 score of 7.5 (High) and a CVSS v4.0 score of 8.2 (High) (Feedly, GitHub Advisory, VulnCheck).

The root cause is classified as CWE-770 (Allocation of Resources Without Limits or Throttling) and CWE-400 (Uncontrolled Resource Consumption). The RealtimeCallHandler in extensions/voice-call/src/webhook/realtime-handler.ts instantiated a WebSocketServer without specifying a maxPayload limit, meaning arbitrarily large WebSocket frames were accepted and passed to JSON parsing and bridge setup logic before any size check occurred. The fix introduces a 256 KB (MAX_REALTIME_MESSAGE_BYTES = 256 * 1024) hard limit via the maxPayload option on the WebSocketServer, causing oversized frames to be rejected with WebSocket close code 1009 before any downstream processing. Additionally, unhandled ws error events that could crash the gateway are now absorbed (GitHub Advisory, Fix Commit).

Successful exploitation results in a high availability impact — remote attackers can render the voice-call realtime WebSocket service unavailable for all users of affected deployments. There is no confidentiality or integrity impact; the vulnerability is limited to a denial-of-service condition. Only deployments that expose the voice-call realtime WebSocket path externally are at risk (GitHub Advisory, Feedly).

No public exploit code or in-the-wild exploitation has been reported for CVE-2026-42437. The EPSS score is approximately 0.091%, indicating a low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Exploitation requires no authentication, no user interaction, and only network access to the exposed WebSocket endpoint, making it straightforward for any remote attacker to attempt (Feedly).

1. Reconnaissance: Identify internet-facing OpenClaw deployments running npm package version >= 2026.4.9 and < 2026.4.10 that expose the voice-call realtime WebSocket path (e.g., via Shodan, Censys, or direct probing).
2. Establish WebSocket connection: Connect to the target's voice-call realtime WebSocket endpoint (e.g., wss://<target>/voice/realtime/<stream-token>) using a WebSocket client such as wscat or a custom script.
3. Send oversized frame: Transmit a WebSocket frame exceeding the server's processing capacity — for example, a JSON payload with a start event containing a padding field filled with hundreds of kilobytes of data (e.g., 'A'.repeat(300 * 1024)).
4. Trigger denial of service: The unpatched server accepts and attempts to process the oversized frame, consuming excessive resources or crashing the gateway process, causing service unavailability for all users of the voice-call feature.
5. Repeat as needed: Since no authentication is required, the attacker can repeatedly send oversized frames to sustain the denial-of-service condition (GitHub Advisory, Fix Commit).

• Network: Unusually large WebSocket frames (>256 KB) sent to the voice-call realtime WebSocket endpoint; high-volume or repeated WebSocket connection attempts from a single or rotating set of IP addresses targeting the realtime stream path.
• Logs: Gateway process logs showing [voice-call] realtime WS error: entries with messages related to payload size limits or connection resets; repeated WebSocket upgrade requests to the realtime path followed by abrupt disconnections.
• Process: Elevated memory or CPU usage in the OpenClaw gateway process coinciding with WebSocket traffic spikes; unexpected gateway process crashes or restarts during active voice-call sessions (GitHub Advisory, Fix Commit).

Users should upgrade the OpenClaw npm package to version 2026.4.10 or later; the latest release, 2026.4.14, also includes the fix. The patch enforces a 256 KB maximum payload size (maxPayload: MAX_REALTIME_MESSAGE_BYTES) on the WebSocketServer handling the voice-call realtime path, rejecting oversized frames before any JSON parsing or bridge setup occurs. As a temporary workaround for deployments that cannot immediately upgrade, restricting network access to the voice-call realtime WebSocket endpoint (e.g., via firewall rules or reverse proxy configuration) can reduce exposure (GitHub Advisory, Fix Commit).

The vulnerability was reported by G0odUser from ADLab of VenusTech, and also by @zsxsoft with sponsorship from @KeenSecurityLab and @qclawer. A brief mention was noted on Mastodon via @thehackerwire. No significant broader media coverage or notable community debate has been observed beyond standard CVE aggregator postings (GitHub Advisory, Feedly).