CVE-2026-108698: Time-of-check Time-of-use (TOCTOU) Race Condition in hyper-mcp-rs hyper-mcp

The vulnerability exists in hyper-mcp versions up to 0.8.3 in the load_wasm function located in src/wasm/oci.rs. The function incorrectly verifies the Cosign signature of a separately resolved tag rather than the actual loaded manifest. This TOCTOU race condition allows an attacker controlling registry responses to serve a malicious unsigned manifest to the loader while providing a signed manifest to Cosign verification. Consequently, unsigned WebAssembly plugins can be executed with the privileges configured for the host, bypassing intended signature verification controls.

An attacker able to control registry responses can bypass signature verification and execute unsigned WebAssembly plugins with configured host capabilities. This could lead to execution of malicious code within the host environment, potentially compromising system integrity and security. The CVSS 4.0 score of 8.3 reflects a high severity with network attack vector, low attack complexity, no privileges required, no user interaction, and high impact on integrity and availability.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, users should avoid using affected versions or restrict access to untrusted registries to mitigate risk. Monitor vendor communications for updates on patches or official fixes.