CVE-2026-40351

CriticalPublic PoC

Published: 17 April 2026

Published

17 April 2026

Modified

27 April 2026

KEV Added

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Patch

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CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0007 21.0th percentile

Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-40351 is a critical-severity Improper Neutralization of Special Elements in Data Query Logic (CWE-943) vulnerability in Fastgpt Fastgpt. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 21.0th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

This vulnerability is AI-related — categorised as APIs and Models.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-10 Information Input Validation good match

prevent

Directly requires runtime validation of password inputs at the login endpoint to block NoSQL injection operators like {"$ne": ""} from bypassing authentication.

SI-2 Flaw Remediation good match

prevent

Mandates timely flaw remediation, such as applying the patch in FastGPT v4.14.9.5 that adds runtime validation missing due to TypeScript type assertion.

IA-5 Authenticator Management partial match

prevent

Ensures authenticator management practices verify and protect password strength against injection attacks that bypass login checks.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

NoSQL injection in public-facing login endpoint enables remote authentication bypass for unauthorized access to any account including admin, directly mapping to exploitation of public-facing application for initial access.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

FastGPT is an AI Agent building platform. In versions prior to 4.14.9.5, the password-based login endpoint uses TypeScript type assertion without runtime validation, allowing an unauthenticated attacker to pass a MongoDB query operator object (e.g., {"$ne": ""}) as the password…

field. This NoSQL injection bypasses the password check, enabling login as any user including the root administrator. This issue has been fixed in version 4.14.9.5.

Deeper analysisAI

CVE-2026-40351 is a NoSQL injection vulnerability in FastGPT, an AI Agent building platform, affecting versions prior to 4.14.9.5. The issue occurs in the password-based login endpoint, where TypeScript type assertion is applied without runtime validation of the input. This flaw enables an attacker to submit a MongoDB query operator object, such as {"$ne": ""}, in the password field, bypassing the authentication check entirely. The vulnerability is classified under CWE-943 and carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

An unauthenticated attacker can exploit this vulnerability remotely over the network with low complexity and no user interaction or privileges required. By crafting a malicious password payload, the attacker bypasses login validation and gains unauthorized access as any user account, including the root administrator, potentially compromising the entire platform.

The vulnerability has been fixed in FastGPT version 4.14.9.5. Security advisories recommend upgrading to this patched version to mitigate the issue. Key references include the fixing commit at https://github.com/labring/FastGPT/commit/bd966d479fbe414d02679cf79f9eaaab3d100a2d, the release notes at https://github.com/labring/FastGPT/releases/tag/v4.14.9.5, and the GitHub security advisory at https://github.com/labring/FastGPT/security/advisories/GHSA-x8mx-2mr7-h9xg.