CVE-2026-14916 in API Gateway
Summary
by MITRE • 09/16/2026
A JWT signature verification vulnerability affects Kong components that perform JWT validation for MCP OAuth2 or DataKit integrations inside Kong API Gateway Enterprise. The affected code does not properly validate that the JWT signing algorithm is compatible with the type of key used for verification.
As a result, an unauthenticated remote attacker may be able to craft a forged JWT that is incorrectly accepted as valid, leading to authentication bypass and potential compromise of confidentiality, integrity, and availability.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability identified in Kong API Gateway Enterprise represents a critical flaw within the JSON Web Token (JWT) signature verification logic used for MCP OAuth2 and DataKit integrations. This issue stems from an improper validation mechanism that fails to ensure compatibility between the algorithm specified in the JWT header and the type of cryptographic key provided for verification. In secure implementations, it is imperative that the signing algorithm declared by the token issuer matches the capabilities of the verifier's key material. For instance, if a public RSA key is used, the system must strictly enforce algorithms like RS256 or ES256 depending on the key type, rather than allowing any arbitrary algorithm to be processed against it. The absence of this strict binding allows an attacker to manipulate the JWT header fields to specify an algorithm that behaves differently during verification, potentially bypassing cryptographic checks entirely.
This technical flaw directly enables authentication bypass by allowing unauthenticated remote attackers to forge valid-looking tokens without possessing the correct private signing key. By crafting a malicious JWT with a manipulated algorithm field and corresponding signature structure, the attacker can trick the Kong gateway into accepting the token as legitimate. This failure in input validation aligns closely with CWE-347, which describes Improper Verification of Cryptographic Signature, and is further contextualized by MITRE ATT&CK technique T1652, Client-side Impersonation. The ability to forge tokens undermines the fundamental trust model of API gateways, where authentication integrity relies on the assumption that only holders of private keys can generate valid signatures for public key verification scenarios.
The operational impact of this vulnerability is severe, as it compromises the confidentiality, integrity, and availability of services protected by Kong. Once an attacker successfully authenticates using a forged token, they gain unauthorized access to backend APIs and data resources intended for legitimate users or service accounts. This can lead to data exfiltration, modification of critical business logic through API manipulation, and potential lateral movement within the network infrastructure if the compromised credentials have elevated privileges. Furthermore, because this affects core authentication components like MCP OAuth2 and DataKit integrations, the blast radius extends across all downstream services relying on these specific integration points for identity verification.
To mitigate this risk, organizations running Kong API Gateway Enterprise must apply the latest security patches provided by Kong that address the JWT validation logic. It is essential to ensure that the gateway software version includes fixes for algorithm binding and strict key-type matching during signature verification. Administrators should also review their current configurations to verify that no custom plugins or overrides are bypassing these standard validation checks. Additionally, implementing defense-in-depth strategies such as rigorous input sanitization at the application layer and monitoring for anomalous authentication patterns can provide supplementary protection against exploitation attempts while patch management is being executed.