CVE-2026-0621: Anthropic's MCP TypeScript SDK has a ReDoS vulnerability
(updated )
A ReDoS vulnerability in the UriTemplate class allows attackers to cause denial of service. The partToRegExp() function generates a regex pattern with nested quantifiers (([^/]+(?:,[^/]+)*)) for exploded template variables (e.g., {/id*}, {?tags*}), causing catastrophic backtracking on malicious input.
Who is affected: MCP servers that register resource templates with exploded array patterns and accept requests from untrusted clients.
Attack result: An attacker sends a crafted URI via resources/read request, causing 100% CPU utilization, server hang/crash, and denial of service for all clients.
References
- github.com/advisories/GHSA-8r9q-7v3j-jr4g
- github.com/modelcontextprotocol/typescript-sdk/commit/7f0cf730
- github.com/modelcontextprotocol/typescript-sdk/commit/b392f02ffcf37c088dbd114fedf25026ec3913d3
- github.com/modelcontextprotocol/typescript-sdk/issues/965
- github.com/modelcontextprotocol/typescript-sdk/releases/tag/v1.25.2
- github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-cqwc-fm46-7fff
- nvd.nist.gov/vuln/detail/CVE-2026-0621
- www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos
Code Behaviors & Features
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