{"id":"CVE-2026-80347","state":"PUBLISHED","title":"mcp-fetch through 1.6.3 Server-Side Request Forgery via Unstripped IPv6 Literal Brackets","description":"mcp-fetch checks a fetch target against its SSRF guard without removing the brackets that surround an IPv6 literal. isSafeUrl reads the hostname from the parsed URL, which for a literal such as http://[::1]/ yields the bracketed string, and then tests it with net.isIP. That call returns zero for a bracketed value, so the branch holding the private-address checks is skipped entirely. The guard falls back to resolving the hostname, the bracketed string is not a resolvable name, no addresses are returned, and the target is reported safe. The HTTP client then strips the brackets and connects. Because the address may be given in IPv4-mapped form, the same path reaches any IPv4 target the loopback and private checks were meant to exclude, including link-local metadata endpoints. isPrivateIPv6 also has no case for the ::ffff: prefix, so the mapped form would still pass even if the brackets were removed. The fetch target is supplied as a tool argument, so an attacker who can influence what the model requests can read internal responses back into the model context.","publishedAt":"2026-08-26T10:09:47.977Z","updatedAt":"2026-08-26T12:05:24.996Z","severity":{"score":8.7,"label":"High","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N","source":"VulnCheck"},"assigner":"VulnCheck","products":["kazuph mcp-fetch"],"affected":[{"vendor":"kazuph","product":"mcp-fetch","packageURL":"pkg:npm/%40kazuph/mcp-fetch","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThanOrEqual":"1.6.3","versionType":"semver"}],"collectionURL":"https://github.com/kazuph/mcp-fetch","repo":"https://github.com/kazuph/mcp-fetch"}],"references":["https://github.com/kazuph/mcp-fetch","https://github.com/kazuph/mcp-fetch/issues/16","https://www.npmjs.com/package/@kazuph/mcp-fetch","https://www.vulncheck.com/advisories/mcp-fetch-through-1.6.3-server-side-request-forgery-via-unstripped-ipv6-literal-brackets"],"weaknesses":["CWE-918"],"ingestedAt":"2026-10-29T20:13:07.220Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/80xxx/CVE-2026-80347.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-80347","state":"PUBLISHED","datePublished":"2026-08-26T10:09:47.977Z","dateUpdated":"2026-08-26T12:05:24.996Z","assignerShortName":"VulnCheck","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","dateReserved":"2026-08-26T09:56:49.602Z"},"containers":{"cna":{"title":"mcp-fetch through 1.6.3 Server-Side Request Forgery via Unstripped IPv6 Literal Brackets","descriptions":[{"lang":"en","value":"mcp-fetch checks a fetch target against its SSRF guard without removing the brackets that surround an IPv6 literal. isSafeUrl reads the hostname from the parsed URL, which for a literal such as http://[::1]/ yields the bracketed string, and then tests it with net.isIP. That call returns zero for a bracketed value, so the branch holding the private-address checks is skipped entirely. The guard falls back to resolving the hostname, the bracketed string is not a resolvable name, no addresses are returned, and the target is reported safe. The HTTP client then strips the brackets and connects. Because the address may be given in IPv4-mapped form, the same path reaches any IPv4 target the loopback and private checks were meant to exclude, including link-local metadata endpoints. isPrivateIPv6 also has no case for the ::ffff: prefix, so the mapped form would still pass even if the brackets were removed. The fetch target is supplied as a tool argument, so an attacker who can influence what the model requests can read internal responses back into the model context."}],"affected":[{"vendor":"kazuph","product":"mcp-fetch","packageURL":"pkg:npm/%40kazuph/mcp-fetch","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThanOrEqual":"1.6.3","versionType":"semver"}],"collectionURL":"https://github.com/kazuph/mcp-fetch","repo":"https://github.com/kazuph/mcp-fetch"}],"references":[{"url":"https://github.com/kazuph/mcp-fetch","tags":["product"]},{"url":"https://github.com/kazuph/mcp-fetch/issues/16","tags":["issue-tracking"]},{"url":"https://www.npmjs.com/package/@kazuph/mcp-fetch","tags":["product"]},{"url":"https://www.vulncheck.com/advisories/mcp-fetch-through-1.6.3-server-side-request-forgery-via-unstripped-ipv6-literal-brackets","name":"VulnCheck Advisory: mcp-fetch through 1.6.3 Server-Side Request Forgery via Unstripped IPv6 Literal Brackets","tags":["third-party-advisory"]}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"HIGH","subConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","subIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED","version":"4.0","baseSeverity":"HIGH","baseScore":8.7,"vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"}},{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV3_1":{"attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"NONE","availabilityImpact":"NONE","version":"3.1","baseSeverity":"HIGH","baseScore":7.5,"vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-918","lang":"en","description":"Server-Side Request Forgery (SSRF)","type":"CWE"}]}],"providerMetadata":{"shortName":"VulnCheck","orgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","dateUpdated":"2026-08-26T10:09:47.977Z"},"datePublic":"2026-08-26T00:00:00.000Z","credits":[{"lang":"en","value":"George Chen","type":"finder"}],"x_generator":{"engine":"vulncheck-endgame"},"source":{"discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/kazuph/mcp-fetch/issues/16","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-26T12:05:01.381249Z","id":"CVE-2026-80347","options":[{"Exploitation":"poc"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-26T12:05:24.996Z"}}]}}}