{"id":"CVE-2026-80347","title":"mcp-fetch checks a fetch target against its SSRF guard without removing the brackets that surround an IPv6 literal","summary":"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, …","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","cwe":["CWE-918"],"published":"2026-08-26","updated":"2026-09-24","sourceUpdated":"2026-09-24T20:43:32.537","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-80347","references":[{"url":"https://github.com/kazuph/mcp-fetch","label":"disclosure@vulncheck.com"},{"url":"https://github.com/kazuph/mcp-fetch/issues/16","label":"disclosure@vulncheck.com"},{"url":"https://www.npmjs.com/package/@kazuph/mcp-fetch","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/mcp-fetch-through-1.6.3-server-side-request-forgery-via-unstripped-ipv6-literal-brackets","label":"disclosure@vulncheck.com"},{"url":"https://github.com/kazuph/mcp-fetch/issues/16","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"tags":["nvd"],"epss":0.00482,"epssPercentile":0.3887,"ingestedAt":"2026-09-24T20:51:40.230Z","slug":"CVE-2026-80347","body":"## Overview\n\nmcp-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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}