CVE-2026-103471 in restbed
Summary
by MITRE • 09/30/2026
restbed through 5.0.0 buffers HTTP request headers without enforcing a maximum size limit, allowing remote unauthenticated attackers to exhaust server memory. Attackers can open TCP connections and stream bytes indefinitely without sending the header delimiter, forcing the server to allocate unbounded heap memory until the process is killed.
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Analysis
by VulDB Data Team • 09/30/2026
The restbed library through version 5.0.0 contains a critical resource exhaustion vulnerability stemming from an improper implementation of HTTP request parsing logic. Specifically, the component fails to enforce a maximum size limit on incoming HTTP request headers during the initial phase of connection handling. This design flaw allows remote unauthenticated attackers to exploit the server by opening TCP connections and streaming arbitrary bytes indefinitely without transmitting the required header delimiter sequence that signals the end of the header block. Because the library attempts to buffer these incoming bytes in memory while waiting for the termination signal, it allocates heap space continuously as more data arrives from the client side.
This behavior creates a direct path to Denial of Service conditions through resource exhaustion. Since there is no upper bound on the amount of memory allocated per connection or globally for header buffers, an attacker can force the server process to consume all available system RAM. The operational impact is severe, as the unbounded allocation eventually leads to out-of-memory errors, causing the application to crash or become unresponsive. This effectively renders the service unavailable to legitimate users and may require manual intervention or automatic restart mechanisms to restore functionality, thereby impacting availability metrics significantly.
From a classification perspective, this vulnerability aligns with CWE-789: Memory Allocation with Unlimited Input, which describes scenarios where software allocates memory based on user input without validating that the size is within expected bounds. It also relates closely to CWE-400: Uncontrolled Resource Consumption, as the attacker controls the rate and volume of resource usage by simply maintaining an open connection and sending data. In terms of offensive security frameworks, this technique corresponds to MITRE ATT&CK T1498: Network Denial of Service, specifically under sub-techniques involving volumetric attacks or protocol abuse where the goal is to overwhelm system resources rather than exploit a logic flaw for privilege escalation.
Mitigation strategies should focus on implementing strict limits at both the application and infrastructure levels. Developers must configure restbed to enforce a maximum header size limit that aligns with standard HTTP specifications, such as RFC 7230, which suggests reasonable limits like eight kilobytes or less per line of headers. Additionally, setting timeouts for incomplete requests is crucial; if a client fails to send the complete header block within a defined timeframe, the connection should be terminated immediately to prevent further memory allocation. Infrastructure-level protections such as reverse proxies can also help by enforcing request size limits and dropping connections that exceed these thresholds before they reach the application server, thereby providing an additional layer of defense against this type of resource exhaustion attack.