CVE-2026-100527 in OpenClaw
Summary
by MITRE • 09/26/2026
OpenClaw before 2026.8.2 contains a denial of service vulnerability in the Browser extension relay that allows unauthenticated network sources to exhaust pending-authentication capacity. Attackers can hold every pending slot by maintaining silent WebSocket upgrades, preventing paired extensions from completing Browser Relay Authentication v2.
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Analysis
by VulDB Data Team • 09/26/2026
The identified vulnerability resides within the OpenClaw software suite prior to version 2026.8.2, specifically affecting the mechanism responsible for relaying traffic through browser-based interfaces. This flaw is classified as a denial of service condition that targets the authentication infrastructure rather than the application logic itself. The core issue lies in how the system manages pending authentication states during WebSocket upgrade procedures. When an unauthenticated network source initiates a connection request, the server allocates internal resources to track and process this pending state. However, due to insufficient validation or resource management controls, these allocated slots are not properly released if the client ceases communication after initiating the handshake but before completing full authentication.
From a technical perspective, the vulnerability exploits the lifecycle of WebSocket connections within the relay service. An attacker can initiate multiple simultaneous connection requests that trigger the pending-authentication state allocation. By maintaining these connections in an active yet silent state—essentially keeping the TCP and WebSocket layers open without sending further data or completing the authentication handshake—the attacker effectively locks these resource slots. The system interprets this silence as a valid, albeit slow-moving, client session rather than a malicious stall attempt. Consequently, every available slot for pending-authentication is consumed by these phantom sessions. This behavior aligns with CWE-400, which describes uncontrolled resource consumption, and specifically relates to the failure to enforce proper connection limits or timeouts during the authentication phase.
The operational impact of this vulnerability is severe for users relying on paired extensions that utilize Browser Relay Authentication v2. Since the pending-authentication capacity is finite, once all slots are exhausted by an attacker's silent connections, legitimate users cannot establish new relay sessions. This results in a complete denial of service for authenticated extension pairs attempting to communicate through the relay. The inability to complete authentication means that critical data synchronization or remote control functionalities dependent on this channel become unavailable until the stale connections time out naturally or are manually cleared by an administrator. This disruption can hinder productivity and compromise the availability of services that depend on real-time browser-to-application communication channels.
This attack vector is consistent with techniques observed in ATT&CK framework mappings, particularly those involving resource exhaustion to disrupt service availability. The attacker leverages unauthenticated access, which corresponds to initial access or reconnaissance phases depending on whether prior enumeration was performed, but the primary effect is a denial of service that impacts system availability. To mitigate this risk, it is imperative for organizations running OpenClaw versions earlier than 2026.8.2 to apply the vendor-provided patch immediately. The updated version likely implements stricter timeouts for pending authentication states and enforces limits on concurrent unauthenticated connections from single or distributed sources. Until patches are applied, administrators should consider implementing network-level rate limiting or firewall rules that restrict WebSocket upgrade requests to known IP ranges if feasible, thereby reducing the attack surface available to unauthenticated actors attempting to exhaust system resources.