{"id":"CVE-2026-80347","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-80347","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…","details":"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.","published":"2026-08-26T10:16:42.803","modified":"2026-08-26T13:19:24.960","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[],"fix":null,"references":[{"type":"WEB","url":"https://github.com/kazuph/mcp-fetch"},{"type":"WEB","url":"https://github.com/kazuph/mcp-fetch/issues/16"},{"type":"WEB","url":"https://www.npmjs.com/package/@kazuph/mcp-fetch"},{"type":"WEB","url":"https://www.vulncheck.com/advisories/mcp-fetch-through-1.6.3-server-side-request-forgery-via-unstripped-ipv6-literal-brackets"},{"type":"WEB","url":"https://github.com/kazuph/mcp-fetch/issues/16"}],"provenance":{"sources":["OSV.dev","NVD","FIRST.org (EPSS)"],"lastVerified":"2026-08-26T13:19:24.960"}}