x64dbg-MCP Server CVE-2026-107820

Requires an affected version (prior to 1.2) of the x64dbg-MCP Server plugin running with x64dbg, reachable over the network - trivially satisfied by default since pre-1.2 versions bind the HTTP listener to 0.0.0.0. No authentication is needed because the unbounded Content-Length is parsed in wsRecv() before the token check. The key limiting factor is build configuration: the integer-overflow panic that causes the crash only occurs in Debug and ReleaseSafe builds; a ReleaseFast build would not panic. Exploitation also obviously requires that an operator has the plugin installed and an active debugging session worth disrupting.

This is a genuine but low-urgency issue. The CVSS vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L, base 5.3 MEDIUM) is internally consistent with the description: the server listens on 0.0.0.0 by default in affected versions and the overflow is reached in wsRecv() before token authentication, so an unauthenticated network client can trigger it with low complexity. Crucially, impact is bounded to availability only (C:N/I:N/A:L) - the description and source diff confirm the overflowed value feeds only a comparison, so there is no memory corruption or code execution despite the CWE-190 classification and the 'RCE'/'Buffer Overflow' tags. No EPSS score, CISA KEV listing, POC, or SSVC data was provided; absence of these is consistent with a newly-disclosed, low-footprint tool and not evidence of active exploitation. A further real-world limiter not reflected in the CVSS score: the panic only fires in Debug and ReleaseSafe Zig builds - a ReleaseFast production build would wrap silently rather than crash, so exploitability depends on how the plugin was compiled. Net: a real, fix-worthy DoS, but not a priority for most defenders given the niche product and DoS-only impact.

An attacker on the same network (or the internet, since the server binds 0.0.0.0 by default pre-1.2) sends a single crafted HTTP request to the MCP port with a near-maximum Content-Length header. The unchecked usize addition in wsRecv() overflows and triggers a Zig runtime panic, instantly terminating the x64dbg process and any live debugging session. No authentication token is required because the overflow occurs before the auth check; no public exploit code was identified at time of analysis.