GHSA-8R9Q-7V3J-JR4G

Vulnerability from github – Published: 2026-01-05 21:30 – Updated: 2026-01-07 16:16
VLAI?
Summary
Anthropic's MCP TypeScript SDK has a ReDoS vulnerability
Details

Impact

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.

Affected Versions

All versions of @modelcontextprotocol/sdk prior to the patched release.

Patches

v1.25.2 contains b392f02ffcf37c088dbd114fedf25026ec3913d3 the fix modifies the regex pattern to prevent backtracking.

Workarounds

  • Avoid using exploded patterns ({/id*}, {?tags*}) in resource templates
  • Implement request timeouts and rate limiting
  • Validate URIs before processing to reject suspicious patterns
Severity ?
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "@modelcontextprotocol/sdk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.25.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-0621"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-06T21:20:37Z",
    "nvd_published_at": "2026-01-05T21:16:14Z",
    "severity": "HIGH"
  },
  "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",
  "id": "GHSA-8r9q-7v3j-jr4g",
  "modified": "2026-01-07T16:16:27Z",
  "published": "2026-01-05T21:30:33Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-cqwc-fm46-7fff"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-0621"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/issues/965"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/commit/b392f02ffcf37c088dbd114fedf25026ec3913d3"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/v1.25.2"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Anthropic\u0027s MCP TypeScript SDK has a ReDoS vulnerability"
}


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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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