CVE-2026-41405: OpenClaw DoS Vulnerability

CVE-2026-41405 Overview

OpenClaw before version 2026.3.31 contains a resource exhaustion vulnerability in its MS Teams webhook handling. The application parses webhook request bodies before performing JWT validation, allowing unauthenticated attackers to trigger resource exhaustion by sending specially crafted Teams webhook payloads. This bypass of authentication checks enables remote attackers to exhaust server resources without any credentials.

Critical Impact

Unauthenticated remote attackers can cause denial of service by exhausting server resources through malicious MS Teams webhook payloads, potentially disrupting critical business communications and integrations.

Affected Products

• OpenClaw versions prior to 2026.3.31
• Systems with MS Teams webhook integration enabled
• Deployments accepting external webhook requests

Discovery Timeline

• 2026-04-28 - CVE CVE-2026-41405 published to NVD
• 2026-04-28 - Last updated in NVD database

Technical Details for CVE-2026-41405

Vulnerability Analysis

This vulnerability falls under CWE-408 (Improper Handling of Exception Conditions), specifically manifesting as a resource exhaustion condition in OpenClaw's MS Teams webhook endpoint. The core issue lies in the order of operations during request processing—the application parses and processes the webhook request body before validating the JWT token that should authenticate the request.

This design flaw creates a window where any unauthenticated user can submit requests that consume server resources (CPU, memory, and potentially I/O) during the parsing phase. Since authentication checks occur after resource-intensive parsing operations, attackers can repeatedly send malicious payloads to exhaust server capacity without ever needing valid credentials.

The network-accessible nature of webhook endpoints means this vulnerability can be exploited remotely with no user interaction required. A sustained attack could render the OpenClaw service unavailable, impacting MS Teams integration functionality and potentially affecting dependent systems.

Root Cause

The root cause is an improper sequence of security controls in the webhook request handling pipeline. Authentication via JWT validation should occur as the first step in request processing, before any resource-intensive operations like body parsing. By performing parsing first, the application exposes itself to abuse from unauthenticated sources.

This architectural anti-pattern violates the principle of fail-fast security, where authentication and authorization checks should gate access to any resource-consuming functionality. The fix requires reordering the request handling to validate JWT tokens before parsing webhook payloads.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying an OpenClaw instance with MS Teams webhook integration enabled
2. Crafting malicious webhook payloads designed to maximize parsing overhead
3. Sending repeated requests to the webhook endpoint
4. Bypassing authentication since JWT validation occurs after body parsing
5. Exhausting server resources through accumulated parsing operations

The vulnerability is particularly dangerous because webhook endpoints are typically exposed to external networks to receive legitimate MS Teams notifications, making them readily accessible to attackers.

Detection Methods for CVE-2026-41405

Indicators of Compromise

• Unusual spike in requests to MS Teams webhook endpoints from single or distributed IP addresses
• High CPU or memory utilization on OpenClaw servers without corresponding legitimate traffic increase
• Failed JWT validation logs appearing after evidence of resource-intensive processing
• Service degradation or unavailability coinciding with webhook endpoint activity

Detection Strategies

• Monitor request rates to webhook endpoints and alert on anomalous patterns
• Implement rate limiting at the network edge before requests reach OpenClaw
• Configure application performance monitoring to detect resource exhaustion conditions
• Review access logs for repeated unauthenticated requests to webhook paths

Monitoring Recommendations

• Deploy web application firewall (WAF) rules to detect and block suspicious webhook traffic
• Enable detailed logging of webhook endpoint access including request sizes and processing times
• Set up automated alerts for resource utilization thresholds on OpenClaw servers
• Monitor for service health degradation patterns indicative of DoS conditions

How to Mitigate CVE-2026-41405

Immediate Actions Required

• Upgrade OpenClaw to version 2026.3.31 or later immediately
• Implement rate limiting on MS Teams webhook endpoints at the network perimeter
• Consider temporarily disabling MS Teams webhook integration if upgrade is not immediately possible
• Monitor for exploitation attempts using the detection strategies outlined above

Patch Information

The vulnerability is addressed in OpenClaw version 2026.3.31. The fix reorders the request handling pipeline to perform JWT validation before body parsing, ensuring unauthenticated requests are rejected without consuming parsing resources. Details of the fix can be found in the GitHub commit.

Additional information is available in the GitHub Security Advisory and the VulnCheck Advisory.

Workarounds

• Deploy a reverse proxy or API gateway in front of OpenClaw to enforce rate limiting on webhook endpoints
• Configure network-level access controls to restrict webhook endpoint access to known MS Teams IP ranges
• Implement request size limits to reduce the impact of oversized malicious payloads
• Use a WAF to filter suspicious webhook requests before they reach the application

# Example rate limiting configuration for nginx reverse proxy
# Limit webhook endpoint to 10 requests per second per IP
limit_req_zone $binary_remote_addr zone=webhook:10m rate=10r/s;

location /api/webhooks/teams {
    limit_req zone=webhook burst=20 nodelay;
    proxy_pass http://openclaw_backend;
}