Anthropic's MCP TypeScript SDK has a ReDoS vulnerability
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
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | @modelcontextprotocol/sdk | >= 1.3.0, < 1.25.2 | 1.25.2 |
References
- https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-cqwc-fm46-7fff
- https://nvd.nist.gov/vuln/detail/CVE-2026-0621
- https://github.com/modelcontextprotocol/typescript-sdk/issues/965
- https://github.com/modelcontextprotocol/typescript-sdk/commit/7f0cf730
- https://github.com/modelcontextprotocol/typescript-sdk/commit/b392f02ffcf37c088dbd114fedf25026ec3913d3
- https://github.com/modelcontextprotocol/typescript-sdk
- https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/v1.25.2
- https://www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos
- CVSS vector
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- Weakness (CWE)
CWE-1333- Platform
- npm
- Package
@modelcontextprotocol/sdk- Disclosed
- 05.01.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-8r9q-7v3j-jr4g - CC BY 4.0
Vulnerability history: @modelcontextprotocol/sdk
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 8
- First → latest
- 12.2025 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 6
- Medium 2
Disclosures per year
- 2025: 1
- 2026: 7
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Anthropic's MCP TypeScript SDK has a ReDoS vulnerability this entry
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