Unauthenticated Integer-Overflow DoS in x64dbg-mcp-server Content-Length (CVE-2026-107820)

Vulnerability Overview Title: Unauthenticated pre-auth integer-overflow denial of service via Content-Length in the MCP HTTP receive path Description: Software: x64dbg-mcp-server Affected Versions: <= 1.1 Fixed Versions: 1.2 Severity: 5.3 / 10 (Moderate) Issue Description: x64dbg-mcp-server runs an MCP server within the x64dbg process, exposing debugger operations via HTTP. The HTTP receive path contains an unauthenticated integer overflow vulnerability that causes the entire x64dbg process to crash. The issue lies in the function within handling, which accepts any value without an upper limit. In the x64 build, the parsed value is subsequently used in at . When is close to 2^64-1, the expression overflows . In the default build (dbg), this results in an assertion failure and terminates the entire x64dbg process. This vulnerability can be exploited without authentication and is not affected by Bearer-token checks. Impact: Denial of Service. The vulnerability is used only on the right side of a comparison and does not lead to memory corruption or code execution. Real-world severity ranges from low to moderate, depending on availability. Since the debugger model is considered untrusted, anyone who can open a socket, or anyone on the same network given the default binding to 0.0.0.0, can crash x64dbg to disrupt or evade analysis. Remediation: Place an upper bound on , such as rejecting any values greater than the current buffer size, or using saturating addition or and handling the error at line 431. Binding to 127.0.0.1 by default instead of 0.0.0.0 also reduces exposure. Affected Scope Affected Versions: <= 1.1 Fixed Versions: 1.2 CVSS v3 Base Metrics: - Attack Vector: Network - Attack Complexity: Low - Privileges Required: None - User Interaction: None - Scope: Unchanged - Confidentiality: None - Integrity: None - Availability: Low Remediation Recommended Fix: - Place an upper bound on , such as rejecting any values greater than the current buffer size, or using saturating addition or and handling the error at line 431. - Binding to 127.0.0.1 by default instead of 0.0.0.0 also reduces exposure. POC Code Additional Information CVE ID: CVE-2026-107820 Weakness: CWE-190 Reporter: utiejbadwane Summary This vulnerability is an unauthenticated integer overflow that can cause the x64dbg process to crash. Affected versions are <= 1.1, and the fixed version is 1.2. It is recommended to fix this vulnerability by setting an upper limit for and binding to 127.0.0.1 by default.

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Unauthenticated Integer-Overflow DoS in x64dbg-mcp-server Content-Length (CVE-2026-107820)

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