CVE-2026-42420 Overview
CVE-2026-42420 affects OpenClaw versions prior to 2026.4.8. The vulnerability stems from improper input validation in base64 decode paths. OpenClaw allocates memory before enforcing decoded-size limits, allowing attackers to trigger memory exhaustion through crafted base64-encoded input. Multiple code paths are affected, and authenticated network attackers can exploit them to cause denial of service. The issue is tracked under [CWE-770: Allocation of Resources Without Limits or Throttling].
Critical Impact
Authenticated attackers can submit crafted base64 payloads to exhaust available memory, degrading availability of OpenClaw deployments.
Affected Products
- OpenClaw (Node.js distribution) versions before 2026.4.8
- Deployments exposing base64-decoding endpoints to authenticated users
- Applications embedding the vulnerable OpenClaw component
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
The vulnerability resides in OpenClaw's base64 decoding routines. The code reserves memory buffers based on attacker-controlled length values from the encoded input. Decoded-size limits are not enforced before allocation occurs. An attacker can submit small base64 inputs that declare large decoded sizes or repeatedly invoke decode paths to drive the host into memory exhaustion. Because the flaw exists across multiple code paths, narrow input filtering on a single endpoint is insufficient. The result is a denial-of-service condition affecting process or host availability.
Root Cause
The root cause is improper input validation classified under [CWE-770]. OpenClaw allocates resources before validating their bounds. The decoder trusts size metadata derived from the encoded payload and skips checks against a reasonable maximum. This pattern violates the principle of validating untrusted input before resource commitment.
Attack Vector
Exploitation requires network access and low-level authentication. No user interaction is needed. An attacker submits crafted base64 strings to any of the affected decode paths. The application allocates oversized buffers or repeatedly large allocations, exhausting available memory. The integrity and confidentiality of stored data are not affected — only availability is impacted.
The vulnerability mechanism is detailed in the VulnCheck Advisory and the GitHub Security Advisory GHSA-ccx3-fw7q-rr2r. No public proof-of-concept exploit is currently available.
Detection Methods for CVE-2026-42420
Indicators of Compromise
- Unexplained spikes in process memory consumption on hosts running OpenClaw
- Repeated incoming requests carrying unusually large or anomalously structured base64 payloads
- Out-of-memory (OOM) terminations or container restarts correlated with decode activity
- Authenticated session traffic generating disproportionate decode workload
Detection Strategies
- Inspect application logs for base64 decode operations failing with allocation or OOM errors
- Correlate authenticated API requests with subsequent memory growth in OpenClaw worker processes
- Apply request-size limits at the reverse proxy and alert on payloads exceeding policy thresholds
- Monitor Node.js runtime metrics such as heap usage and event loop lag for anomalous patterns
Monitoring Recommendations
- Track resident set size (RSS) and heap allocation per OpenClaw process at one-minute granularity
- Alert on repeated OOM-killer events targeting the OpenClaw service
- Log and review authentication events preceding memory anomalies to identify abusive accounts
- Enable rate limiting on endpoints invoking base64 decoding and alert on rate-limit breaches
How to Mitigate CVE-2026-42420
Immediate Actions Required
- Upgrade OpenClaw to version 2026.4.8 or later, which enforces decoded-size limits before allocation
- Inventory all deployments of the openclaw:openclaw component and prioritize internet-exposed instances
- Revoke or rotate credentials for any low-privilege accounts that exhibit anomalous decode activity
- Apply request-size caps at the load balancer or API gateway as a compensating control
Patch Information
The fix is published in commit d7c3210cd6f5fdfdc1beff4c9541673e814354d5 and documented in the GitHub Security Advisory GHSA-ccx3-fw7q-rr2r. Update via npm install openclaw@2026.4.8 or pin the upgraded version in package.json and rebuild affected services.
Workarounds
- Enforce a strict maximum body size on endpoints that consume base64 input
- Place OpenClaw services behind a reverse proxy that rejects payloads above a defined threshold
- Restrict access to authenticated decode endpoints to trusted user groups until patching is complete
- Configure container memory limits and automatic restart policies to contain exhaustion attempts
# Configuration example
# Upgrade OpenClaw to the patched release
npm install openclaw@2026.4.8
# Example nginx request-size cap as a compensating control
# /etc/nginx/conf.d/openclaw.conf
client_max_body_size 256k;
# Example Node.js process memory limit
node --max-old-space-size=512 server.js
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
