CVE-2026-100558 in OpenClaw
Summary
by MITRE • 09/26/2026
OpenClaw versions before 2026.8.1 contain a resource exhaustion vulnerability in the Gateway listener that allows unauthenticated clients to retain response sockets by sending WebSocket upgrade requests without matching connection semantics. Attackers can repeatedly send malformed upgrade requests to exhaust listener resources and cause denial of service without consuming the WebSocket pre-auth connection budget.
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Analysis
by VulDB Data Team • 09/26/2026
The identified vulnerability resides within the OpenClaw Gateway listener component, specifically affecting versions prior to 2026.8.1. This flaw represents a critical resource exhaustion issue that stems from an improper handling of WebSocket upgrade requests by unauthenticated clients. In standard network operations, when a client initiates a connection using the HTTP Upgrade protocol to transition into a persistent WebSocket session, the server is expected to validate the request against established security policies and connection limits before allocating significant backend resources. However, in this specific implementation, the Gateway listener fails to enforce strict semantic matching for these upgrade requests from unauthenticated sources. This architectural oversight allows malicious actors to bypass standard authentication gates that would normally limit resource consumption based on user identity or pre-authenticated session budgets.
The technical mechanism of exploitation involves an attacker repeatedly sending malformed WebSocket upgrade requests to the target service. Because the listener does not properly validate whether the incoming request adheres to the expected connection semantics, it proceeds with partial initialization steps required for a WebSocket handshake without completing the full authentication process. Crucially, these operations do not consume the designated pre-authentication connection budget that is typically used to throttle unauthenticated traffic and prevent abuse. As a result, each malformed request consumes backend resources such as file descriptors, memory buffers, or thread pool slots associated with maintaining response sockets. Since there is no effective cap on this specific type of resource allocation for invalid upgrade attempts, an attacker can trigger these allocations at a high rate, leading to rapid depletion of available system resources.
The operational impact of this vulnerability is severe, primarily manifesting as a denial of service condition. By exhausting the listener's capacity to handle new connections or maintain existing ones, the attack renders the OpenClaw Gateway unresponsive to legitimate traffic. This effectively disrupts availability for all users attempting to access services hosted behind the gateway. Unlike traditional volumetric attacks that rely on bandwidth saturation, this is a logic-based resource exhaustion attack that targets application-layer efficiency. The ability to bypass pre-auth connection limits makes this particularly dangerous in environments where rate limiting or quota systems are relied upon as primary defenses against abuse from untrusted networks.
From a classification perspective, this vulnerability aligns with CWE-400, which covers Uncontrolled Resource Consumption, and more specifically CWE-770: Allocation of Resources Without Limits or Throttling within the same context. In terms of offensive security frameworks such as MITRE ATT&CK, this behavior is consistent with techniques found under T1499 Endpoint Denial of Service, particularly where an attacker leverages application logic flaws to degrade service availability rather than exploiting a buffer overflow or crash condition directly. The lack of proper input validation and resource accounting for WebSocket upgrade requests highlights a gap in the defense-in-depth strategy employed by the software.
To mitigate this vulnerability, organizations running OpenClaw versions before 2026.8.1 should prioritize upgrading to version 2026.8.1 or later as soon as possible. This update addresses the underlying logic error that permits unauthenticated clients to retain response sockets without proper semantic validation. In scenarios where immediate patching is not feasible, administrators can implement network-level controls such as rate limiting on WebSocket upgrade endpoints at the load balancer or reverse proxy layer preceding OpenClaw. Additionally, configuring strict timeouts for incomplete handshake processes and enforcing stricter input filtering on HTTP headers associated with upgrade requests can help reduce the attack surface until a permanent fix is deployed. Regular auditing of connection handling logic in gateway components is also recommended to prevent similar resource exhaustion flaws in future releases.