CVE-2026-14539 in mcp-toolbox
Summary
by MITRE • 07/31/2026
An allocation of resources without limits vulnerability in the HTTP handler component of Google mcp-toolbox versions up to and including 1.4.0 allows an unauthenticated attacker to cause a denial of service (DoS). The /mcp endpoint handler reads incoming payloads directly into system memory using an unrestricted buffer loop (io.ReadAll) without applying defensive constraints such as http.MaxBytesReader or pre-read Content-Length enforcement. By submitting a single, massive HTTP request body, an attacker can linearly consume available host memory until the runtime process is terminated by an Out-Of-Memory (OOM) error.
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Analysis
by VulDB Data Team • 07/31/2026
This vulnerability represents a critical resource exhaustion flaw in Google's mcp-toolbox HTTP handler component affecting versions 1.4.0 and earlier. The issue stems from improper input validation and memory management practices within the /mcp endpoint implementation where the system blindly accepts and processes incoming request payloads without any size limitations or defensive boundaries. The vulnerability specifically manifests through the use of io.ReadAll function which reads entire request bodies into memory without imposing any constraints on the maximum allowable payload size, creating a direct pathway for malicious actors to exploit memory consumption patterns.
The technical exploitation occurs through a straightforward but devastating approach where an unauthenticated attacker can submit a single HTTP request containing an extremely large payload that exceeds normal operational boundaries. The absence of http.MaxBytesReader enforcement or pre-read Content-Length validation means the system processes the entire request body regardless of its size, leading to progressive memory allocation until system resources are exhausted. This pattern aligns with CWE-400 vulnerability classification for unspecified resource exhaustion, where the system fails to properly manage resource consumption limits. The attack vector operates entirely through HTTP protocol manipulation without requiring authentication credentials or complex exploitation techniques.
The operational impact of this vulnerability extends beyond simple service disruption as it can lead to complete system termination through Out-Of-Memory errors that force process crashes and restarts. This denial of service condition affects the availability of the mcp-toolbox service and potentially impacts dependent systems that rely on its functionality. The linear memory consumption pattern means that even moderately sized payloads can cause significant resource exhaustion, making this vulnerability particularly dangerous in environments where multiple concurrent requests could compound the memory pressure. From an ATT&CK framework perspective, this represents a privilege escalation through resource exhaustion technique that can be executed by any remote attacker without authentication requirements.
Mitigation strategies should focus on implementing strict input validation and resource boundary enforcement within the HTTP handler component. The most effective immediate solution involves integrating http.MaxBytesReader to limit payload sizes before processing begins, combined with proper Content-Length header validation to establish pre-defined maximums for request bodies. Additionally, implementing memory monitoring and automatic process restart mechanisms can help detect and recover from memory exhaustion events more gracefully. The fix should also include logging and alerting for unusually large requests that may indicate attempted exploitation, enabling security teams to respond proactively to potential attacks targeting this specific vulnerability pattern.