AWS API MCP Server Vulnerability Bypasses OAuth Checks
The flaw leaves systems open to unauthorized access by failing to validate token audience claims in older versions.
Updated on Oct. 27, 2026 in Cybersecurity
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Security researchers have identified a critical vulnerability in the AWS API MCP Server that permits attackers to bypass OAuth token audience validation. The flaw, designated CVE-2026-115413, affects server versions 1.3.0 through 1.5.9.
Why it matters
The vulnerability exposes a gap in identity verification protocols that could allow unauthorized access to services relying on the AWS API MCP Server. This oversight highlights the necessity for rigorous audience claim validation in OAuth implementations to ensure tokens are used only by their intended recipients.
The vulnerability exists in software versions 1.3.0 through 1.5.9 and specifically involves the omission of an audience claim check within the OAuth authentication flow. While the system verifies the token's signature, issuer, and expiry, it fails to ensure the token was issued for the specific application attempting the connection.
The players
AWS API MCP Server
A server component designed to manage and validate authentication tokens within Amazon Web Services API ecosystems.
The details
The AWS API MCP Server uses OAuth, a standard for access delegation, to authenticate requests. Typically, an identity provider issues a bearer token that includes an audience claim, which identifies the intended recipient application. The vulnerability occurs because the server validates the token's structural integrity but fails to verify this audience claim, allowing an attacker to present a valid token issued for a different service to gain unauthorized access.
Timeline
- 2026-10-27
Vulnerability CVE-2026-115413 was publicly reported.
The Tech Race
This vulnerability fits into the ongoing industry struggle to secure complex, token-based authentication architectures. It mirrors the risks inherent in the 2020 SolarWinds supply chain attack by highlighting how a single failure in identity verification can undermine broader system integrity.
System administrators managing instances of the AWS API MCP Server should review their current version and update to secure releases to prevent potential authentication bypasses. The update is critical for any entity utilizing these versions to maintain strict OAuth compliance and identity isolation.
The takeaway
The oversight in token audience validation underscores the danger of partial compliance in identity protocols. Users should verify their software version immediately and monitor future security bulletins for patch availability.
Further reading
For more on evolving threat vectors and defense strategies, visit Cybersecurity.
Source note: This article includes information reported by IT Security News - cybersecurity, infosecurity news.
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