{"apiVersion":"1.0","identifier":"CVE-2026-80347","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":"2026-08-26T10:16:42","lastModifiedAt":"2026-08-26T13:19:24","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-80347","cvssScore":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","epssProbability":0.00277,"riskScore":0.77,"affectedProduct":"mcp-fetch","affectedVersions":"unknown","vulnerabilityType":"Library","operatingSystems":[],"links":{"self":"https://www.redsauce.net/api/cves/CVE-2026-80347","webPages":{"es":"https://www.redsauce.net/es/cves/CVE-2026-80347","en":"https://www.redsauce.net/en/cves/CVE-2026-80347","fr":"https://www.redsauce.net/fr/cves/CVE-2026-80347","pt":"https://www.redsauce.net/pt/cves/CVE-2026-80347","de":"https://www.redsauce.net/de/cves/CVE-2026-80347","sk":"https://www.redsauce.net/sk/cves/CVE-2026-80347","el":"https://www.redsauce.net/el/cves/CVE-2026-80347"},"source":"https://nvd.nist.gov/vuln/detail/CVE-2026-80347"}}