CVE-2026-35640 in OpenClaw
Summary
by MITRE • 04/10/2026
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 signature rejection.
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Analysis
by VulDB Data Team • 04/10/2026
The vulnerability identified as CVE-2026-35640 affects OpenClaw versions prior to 2026.3.25 and represents a critical security flaw in the webhook processing mechanism that directly impacts system availability and resource management. This issue stems from a fundamental architectural weakness where the system processes JSON payload data before performing authentication and integrity verification checks. The flaw creates a dangerous condition where malicious actors can exploit the order of operations to consume excessive computational resources without proper authorization, effectively creating a pathway for resource exhaustion attacks that can lead to system downtime and service disruption.
The technical implementation of this vulnerability manifests through improper request handling within the webhook processing pipeline where JSON parsing occurs as the initial step in request processing. According to CWE-20, this represents a classic input validation error where the system fails to properly validate input data before processing it. The vulnerability allows attackers to craft malicious webhook requests containing resource-intensive JSON payloads that trigger expensive parsing operations within the server environment. This design flaw violates the principle of least privilege and proper input sanitization, as the system does not validate the authenticity of the request source before allocating computational resources to parse potentially malicious content.
From an operational perspective, this vulnerability creates a significant risk of denial of service conditions that can severely impact system availability and performance. The attack vector enables remote exploitation without requiring authentication credentials, making it particularly dangerous for systems that expose webhook endpoints to untrusted networks. The resource exhaustion occurs through forced JSON parsing operations that can consume substantial memory and CPU cycles, potentially leading to system instability, application crashes, or complete service unavailability. This vulnerability directly maps to ATT&CK technique T1499.004 which describes network disruption attacks targeting availability through resource exhaustion.
The impact of this vulnerability extends beyond simple service disruption as it can potentially enable more sophisticated attack chains where resource exhaustion serves as a precursor to other exploitation techniques. Attackers can leverage this vulnerability to create persistent resource contention that may mask other attacks or make systems more vulnerable to additional exploitation attempts. The timing of the vulnerability is particularly concerning as it occurs at the earliest stage of request processing, meaning that any defensive mechanisms that might otherwise be triggered by authentication failures are bypassed entirely. Organizations implementing OpenClaw versions prior to 2026.3.25 should consider this vulnerability as a critical priority for remediation due to its potential for causing widespread service disruption and its low barrier to exploitation.
Mitigation strategies should focus on implementing proper request ordering where authentication and signature validation occur before any resource-intensive processing takes place. The recommended approach involves updating to OpenClaw version 2026.3.25 or later where the webhook processing pipeline has been redesigned to validate signatures first. Additional defensive measures include implementing rate limiting on webhook endpoints, monitoring for unusual parsing patterns, and configuring resource limits to prevent excessive consumption. Organizations should also consider implementing webhook signature validation at the network level and establishing automated alerting for resource exhaustion events that may indicate exploitation attempts. The fix addresses the core architectural issue by reordering the request processing pipeline to ensure that all authentication checks occur before any computational resources are allocated for payload processing, thereby preventing the resource exhaustion attack vector entirely.