CVE-2026-103472 in Restbed
Summary
by MITRE • 09/30/2026
restbed through 5.0.0 accepts WebSocket frames with declared payload lengths up to 2^63 bytes and buffers the payload without size limits in an unbounded stream buffer. Remote unauthenticated attackers can declare large frame sizes and stream payload data to exhaust server memory, causing denial of service through process crash.
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Analysis
by VulDB Data Team • 09/30/2026
The restbed library, a C++ REST framework for building web services, contains a critical resource exhaustion vulnerability affecting versions up to 5.0.0. This flaw is rooted in the implementation of its WebSocket handler, which fails to enforce strict limits on the size of incoming data frames. Specifically, the application accepts WebSocket frames that declare payload lengths as high as 2^63 bytes, effectively allowing for nearly unlimited memory allocation requests from a single network packet header. The underlying mechanism buffers these payloads into an unbounded stream buffer without performing any preliminary validation against available system resources or predefined configuration thresholds. This architectural oversight creates a direct path for remote attackers to trigger severe performance degradation or complete service failure by manipulating the expected data volume in their communications with the server.
From a technical perspective, this vulnerability represents a classic case of improper input validation leading to resource consumption issues. When an attacker initiates a WebSocket connection and sends frames with extremely large declared payload sizes, the restbed library attempts to allocate memory corresponding to these dimensions. Since there is no upper bound check on the buffer size relative to system constraints or application limits, the server process rapidly consumes available RAM. This behavior aligns closely with CWE-400, which describes conditions where resources are not properly limited before consumption, leading to resource exhaustion. The lack of a maximum frame size configuration option in this version means that even modestly sized but large frames can cumulatively drain memory reserves if sent at sufficient frequency or volume.
The operational impact of exploiting this flaw is severe and immediate for any service relying on restbed for WebSocket communication. A remote, unauthenticated attacker can trigger a denial-of-service condition by simply establishing connections and transmitting these oversized frame declarations. The server process will eventually crash due to out-of-memory errors or become completely unresponsive as it struggles to manage the excessive memory allocation requests. This results in a total loss of availability for legitimate users attempting to connect via WebSocket, effectively taking down the associated web service without requiring any authentication credentials. Such an attack vector is particularly dangerous because it requires minimal effort from the attacker and can be executed with standard networking tools or custom scripts designed to send malformed HTTP/WebSocket traffic.
In terms of threat modeling, this vulnerability facilitates attacks categorized under MITRE ATT&CK technique T1498, Network Denial of Service, specifically through resource exhaustion via unbounded allocation. The attack does not require privilege escalation or complex exploitation chains; it relies solely on the server's willingness to accept and buffer arbitrarily large data structures based on client-provided metadata. This makes it a high-risk vulnerability for any production environment exposing WebSocket endpoints without additional protective layers such as reverse proxies with strict payload size limits, rate limiting mechanisms, or custom middleware that validates frame sizes before they reach the restbed core logic.
To mitigate this risk, organizations using affected versions of restbed should prioritize upgrading to a patched version where input validation and buffer size constraints have been implemented by the maintainers. In environments where immediate patching is not feasible, defensive measures must be applied at the network or application gateway level. Implementing strict limits on WebSocket frame sizes within reverse proxies like Nginx or Apache can prevent oversized frames from reaching the backend server. Additionally, configuring connection rate limiting and monitoring memory usage patterns can help detect and block anomalous traffic indicative of this exploitation attempt. Developers should also review their codebase to ensure that any custom WebSocket handling logic includes explicit checks for payload size against defined maximums before buffer allocation occurs, thereby closing the gap left by the library's default behavior in versions prior to 5.0.1 or later patches addressing CWE-400 and CWE-789 issues related to uncontrolled resource consumption.