CVE-2026-42420: Openclaw Openclaw DOS Vulnerability

CVE-2026-42420 Overview

OpenClaw before version 2026.4.8 contains an improper input validation vulnerability in base64 decode paths that allocate memory before enforcing decoded-size limits. This flaw allows attackers to exploit multiple code paths to cause memory exhaustion or denial of service through crafted base64-encoded input, potentially rendering affected Node.js applications unavailable.

Critical Impact

Attackers can trigger memory exhaustion by sending specially crafted base64-encoded payloads, leading to denial of service conditions in applications using vulnerable OpenClaw versions.

Affected Products

• OpenClaw versions prior to 2026.4.8
• OpenClaw Node.js package

Discovery Timeline

• 2026-04-28 - CVE-2026-42420 published to NVD
• 2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-42420

Vulnerability Analysis

This vulnerability stems from improper input validation in the base64 decoding functionality within OpenClaw. The core issue is that memory allocation occurs before the system validates and enforces limits on the decoded size of incoming data. When processing base64-encoded input, the application allocates memory based on the encoded input size without first checking whether the resulting decoded data would exceed acceptable thresholds.

This design flaw creates a resource exhaustion condition classified as CWE-770 (Allocation of Resources Without Limits or Throttling). An attacker can craft malicious base64-encoded payloads that cause the application to allocate excessive amounts of memory, potentially exhausting available system resources and causing a denial of service condition.

Root Cause

The root cause lies in the order of operations during base64 decoding: memory is allocated based on input characteristics before size validation occurs. The vulnerable code paths process encoded data and allocate corresponding memory buffers without first calculating and validating whether the resulting decoded output would exceed reasonable limits. This allows attackers to force arbitrary memory allocation by controlling the size of base64-encoded input payloads.

Attack Vector

An attacker can exploit this vulnerability remotely over the network by sending crafted base64-encoded data to an application using the vulnerable OpenClaw library. The attack requires low privileges and no user interaction. Multiple code paths within the base64 decode functionality are susceptible, providing various exploitation vectors depending on how the target application processes encoded input.

The security patch addresses DNS pinning behavior in the fetch guard module, optimizing resource handling for trusted environment proxy dispatch:

     try {
       assertExplicitProxySupportsPinnedDns(parsedUrl, params.dispatcherPolicy, params.pinDns);
       await assertExplicitProxyAllowed(params.dispatcherPolicy, params.lookupFn, params.policy);
-      const pinned = await resolvePinnedHostnameWithPolicy(parsedUrl.hostname, {
-        lookupFn: params.lookupFn,
-        policy: params.policy,
-      });
       const canUseTrustedEnvProxy =
         mode === GUARDED_FETCH_MODE.TRUSTED_ENV_PROXY && hasProxyEnvConfigured();
       if (canUseTrustedEnvProxy) {
         dispatcher = createHttp1EnvHttpProxyAgent();
       } else if (params.pinDns === false) {
         dispatcher = createPolicyDispatcherWithoutPinnedDns(params.dispatcherPolicy);
       } else {
+        const pinned = await resolvePinnedHostnameWithPolicy(parsedUrl.hostname, {
+          lookupFn: params.lookupFn,
+          policy: params.policy,
+        });
         dispatcher = createPinnedDispatcher(pinned, params.dispatcherPolicy, params.policy);
       }

Source: GitHub Commit Update

Detection Methods for CVE-2026-42420

Indicators of Compromise

• Abnormal memory consumption spikes in Node.js processes running OpenClaw
• Application crashes or restarts due to out-of-memory conditions
• Unusual patterns of large base64-encoded payloads in incoming requests
• Process termination events correlated with memory exhaustion errors

Detection Strategies

• Monitor Node.js process memory usage for sudden increases or sustained high consumption
• Implement request payload size limits at the network edge to filter oversized base64 inputs
• Deploy application performance monitoring to detect resource exhaustion patterns
• Review application logs for memory allocation failures or heap limit warnings

Monitoring Recommendations

• Configure alerts for memory usage thresholds on systems running OpenClaw-based applications
• Implement rate limiting on endpoints that process base64-encoded data
• Enable detailed logging for request sizes and processing times to identify attack attempts
• Use SentinelOne Singularity Platform to monitor for denial of service attack patterns and anomalous resource consumption

How to Mitigate CVE-2026-42420

Immediate Actions Required

• Upgrade OpenClaw to version 2026.4.8 or later immediately
• Review all applications using OpenClaw for potential exposure
• Implement input size validation at the application layer as an additional safeguard
• Configure resource limits for Node.js processes to contain potential memory exhaustion

Patch Information

The vulnerability has been addressed in OpenClaw version 2026.4.8. The fix ensures that decoded-size limits are enforced before memory allocation occurs during base64 decoding operations. For detailed patch information, refer to the GitHub Security Advisory and the commit containing the fix.

Workarounds

• Implement application-level input validation to reject oversized base64-encoded payloads before they reach OpenClaw
• Configure reverse proxy or WAF rules to limit request body sizes for affected endpoints
• Set Node.js memory limits using --max-old-space-size to prevent complete system resource exhaustion
• Deploy rate limiting to reduce the impact of potential exploitation attempts

# Configuration example - Set Node.js memory limits
node --max-old-space-size=512 your-application.js

# Or via environment variable
export NODE_OPTIONS="--max-old-space-size=512"