Description

MCPHub before 1.0.32 contains an authentication bypass vulnerability in its embedded OAuth 2.0 authorization server where client authentication is disabled by default and PKCE enforcement is optional. Attackers who obtain an authorization code through interception can redeem it for access tokens without providing a client secret or PKCE verifier, gaining access to victim accounts and their privileges.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.8",
  "pubDate": "2026-09-12T11:16:34.483Z",
  "pubdate": "2026-09-12T11:16:34.483Z",
  "executiveSummary": "MCPHub versions prior to 1.0.32 are susceptible to an authentication bypass vulnerability located within the integrated OAuth 2.0 authorization server. The security flaw stems from an insecure default configuration where client authentication mechanisms, specifically client secret verification and Proof Key for Code Exchange (PKCE) enforcement, are not strictly required.\nThis vulnerability allows an unauthenticated attacker to bypass standard authorization flows. By intercepting a valid authorization code, an adversary can successfully exchange it for an access token without satisfying the requisite client-side authentication or integrity checks. Successful exploitation grants the attacker unauthorized access to victim accounts, enabling the abuse of associated privileges and potential compromise of sensitive data.\nThe risk implication is high, as it invalidates the primary security objective of the OAuth 2.0 flow. An attacker does not require elevated privileges or pre-existing credentials to execute this attack, provided they can capture an authorization code through network interception or other means. Organizations utilizing MCPHub versions below 1.0.32 are advised to prioritize remediation to prevent account takeover and unauthorized privilege escalation.",
  "technicalDetails": "The vulnerability resides in the OAuth 2.0 authorization server component of MCPHub, which fails to mandate strict client authentication protocols. In the standard OAuth 2.0 authorization code flow, the exchange of an authorization code for an access token is designed to be secured by either a client secret or, more robustly, through PKCE to mitigate interception risks. MCPHub, however, leaves client authentication disabled by default and makes PKCE enforcement strictly optional for developers, creating a significant security gap.\nThe root cause is an insecure implementation of the token endpoint validation logic. The server component does not enforce the requirement of a client_secret parameter in the token request if the client is registered without strict authentication requirements. Furthermore, because PKCE is not enforced, the server does not validate the code_verifier against the previously stored code_challenge, effectively nullifying the protection PKCE provides against authorization code interception.\nThe attack flow proceeds as follows: First, an attacker intercepts a legitimate authorization code issued by the MCPHub authorization server to a client application. This interception can occur via malicious browser extensions, logs, or man-in-the-middle (MITM) attacks if transport layer security is inadequate. Once the authorization code is acquired, the attacker submits a POST request to the token endpoint of the MCPHub server. The request includes the intercepted authorization code but omits the mandatory client_secret or the code_verifier, relying on the server's misconfiguration to bypass these checks.\nBecause the server component fails to enforce these parameters, it processes the request as a legitimate authorization code redemption. The authorization server returns a valid access token associated with the victim's account to the attacker. Consequently, the attacker assumes the identity of the victim within the application context. The post-exploitation impact is immediate account takeover, as the attacker can perform any action authorized to the victim, bypassing all client-side security controls. This vulnerability affects all MCPHub installations prior to 1.0.32 and requires no specific interaction from the victim beyond the initial authorization request, making it a critical threat to the confidentiality and integrity of user sessions."
}