CVE-2026-11718

The record

An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox. When the toolbox validates an opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), it decodes the response into an introspectResp struct. However, the subsequent claim-checking logic (validateClaims) evaluates the issuer condition as if a.issuer != "" && iss != "". If the external OAuth provider's introspection response omits the optional iss (issuer) field completely, the variable iss defaults to an empty string. This causes the conditional block to evaluate to false and be skipped silently. Consequently, the application accepts tokens issued by unauthorized or unintended third-party identity providers.

Affected packages

Related vulnerabilities

• CVE-2026-114638 Traefik v3.7.0 before v3.7.14 contains an improper authentication vulnerability in the… CWE-287
• CVE-2026-114639 Traefik 2.11.0 before 2.11.58 and 3.0.0 before 3.7.14 contains an authentication bypass… CWE-287
• CVE-2026-112104 A flaw has been found in eremef bandcamp-player up to 1.8.33-beta. CWE-287
• CVE-2026-107228 The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP… CWE-287
• CVE-2026-86781 The SSL Zen — SSL Certificate Installer & HTTPS Redirects WordPress plugin before 4.7.40… CWE-287
• CVE-2026-14563 The advanced-customized-prompts WordPress plugin through 1.0.1 does not verify the… CWE-287
• CVE-2026-14559 The teddy-bear-customize-addon WordPress plugin through 1.0.5 does not verify a user's… CWE-287
• CVE-2026-88895 CyberPanel before 3.0.5 fails to enforce two-factor authentication on API endpoints… CWE-287