CVE-2026-35640
Published: 09 April 2026
Summary
CVE-2026-35640 is a medium-severity Incorrect Behavior Order (CWE-696) vulnerability in Openclaw Openclaw. Its CVSS base score is 6.9 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 31.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and SC-5 (Denial-of-service Protection).
Deeper analysis
CVE-2026-35640 is a denial-of-service vulnerability in OpenClaw versions prior to 2026.3.25. The issue stems from the software parsing JSON request bodies in webhook endpoints before validating signatures, which allows attackers to force resource-intensive parsing operations even on invalid requests. This flaw is classified under CWE-696 (Incorrect Behavior Order: Authorization) and carries a CVSS v3.1 base score of 5.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L), indicating medium severity primarily due to low-impact availability disruption.
Unauthenticated remote attackers can exploit this vulnerability by sending specially crafted malicious webhook requests containing large or complex JSON payloads. Since signature validation occurs after parsing, the server exhausts CPU and memory resources processing these payloads, leading to denial of service through resource exhaustion. No privileges, user interaction, or special access are required, making it accessible to any network adversary targeting exposed OpenClaw webhook endpoints.
Mitigation is addressed in the official GitHub security advisory (GHSA-3h52-cx59-c456) and a corresponding patch commit (5e8cb22176e9235e224be0bc530699261eb60e53), which reportedly reorder operations to validate signatures before JSON parsing. Security practitioners should update to OpenClaw 2026.3.25 or later, as detailed in the advisory and Vulncheck analysis, and review webhook configurations for exposure.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-21136
Vulnerability details
OpenClaw before 2026.3.25 parses JSON request bodies before validating webhook signatures, allowing unauthenticated attackers to force resource-intensive parsing operations. Remote attackers can send malicious webhook requests to trigger denial of service by exhausting server resources through forced JSON parsing before…
more
signature rejection.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability in public-facing webhook endpoints enables remote unauthenticated exploitation via crafted JSON payloads to cause application resource exhaustion and DoS.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Enforces signature validation as an access control mechanism before resource-intensive JSON parsing, directly addressing the incorrect behavior order that enables unauthorized resource exhaustion.
Provides denial-of-service protections such as rate limiting and resource allocation controls to mitigate resource exhaustion from malicious large JSON payloads in webhook requests.
Validates information inputs like webhook signatures and payloads prior to processing to prevent resource-intensive parsing of invalid or oversized JSON.