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The vulnerability exists within the `UriTemplate` class’s URI matching logic when processing RFC 6570 exploded array patterns (e.g., {/list}). The SDK dynamically constructs a regular expression to parse these templates. This generated regex contains nested quantifiers (like (.)) within its pattern-matching groups. When a malicious, specially crafted URI is supplied—typically one with a long, repetitive string segment that fits the initial broad match but fails subsequent conditions—the regex engine enters a state of catastrophic backtracking. It exhaustively attempts all possible permutations of the nested quantifier groups to find a match, causing exponential growth in processing time. This consumes 100% of a single CPU core, rendering the Node.js event loop unresponsive and leading to a complete denial of service for the application.
Platform: Anthropic MCP SDK TypeScript
Version: <= 1.25.1
Vulnerability : Regular Expression DoS
Severity: High
date: 2026-01-05
Prediction: Patch by 2026-01-12
What Undercode Say:
curl -s https://api.github.com/advisories/GHSA-xxxx-xxxx-xxxx | jq '.severity, .affected[].package.ecosystem' npm audit --production Malicious payload pattern for testing: /path?list=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa!
How Exploit:
Attacker sends crafted URI containing long repetitive string to endpoint using vulnerable `UriTemplate` expansion, causing event loop block.
Protection from this CVE
Update to SDK version >1.25.1 when released. Implement request size/time limits. Use alternative URI templating libraries.
Impact:
Application Denial-of-Service, CPU Exhaustion, Unresponsive Node.js Process.
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Sources:
Reported By: github.com
Extra Source Hub:
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