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"CVE-2026-0621"
],
"summary": "Anthropic's MCP TypeScript SDK has a ReDoS vulnerability",
"details": "### Impact\n\nA 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.\n\n**Who is affected:** MCP servers that register resource templates with exploded array patterns and accept requests from untrusted clients.\n\n**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.\n\n### Affected Versions\n\nAll versions of `@modelcontextprotocol/sdk` prior to the patched release.\n\n### Patches\n\nv1.25.2 contains b392f02ffcf37c088dbd114fedf25026ec3913d3 the fix modifies the regex pattern to prevent backtracking.\n\n### Workarounds\n\n- Avoid using exploded patterns (`{/id*}`, `{?tags*}`) in resource templates\n- Implement request timeouts and rate limiting\n- Validate URIs before processing to reject suspicious patterns",
"details": "### Impact\n\nA 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.\n\n**Who is affected:** MCP servers that register resource templates with exploded array patterns and accept requests from untrusted clients.\n\n**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.\n\n### Affected Versions\n\n`@modelcontextprotocol/sdk` versions `>= 1.3.0` and `< 1.25.2` are affected.\n\n### Patches\n\nv1.25.2 contains b392f02ffcf37c088dbd114fedf25026ec3913d3 the fix modifies the regex pattern to prevent backtracking.\n\n### Workarounds\n\n- Avoid using exploded patterns (`{/id*}`, `{?tags*}`) in resource templates\n- Implement request timeouts and rate limiting\n- Validate URIs before processing to reject suspicious patterns",
"severity": [
{
"type": "CVSS_V4",
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