{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "last_affected": "1.6.3"
              }
            ],
            "source": "AFFECTED_FIELD"
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "418e58aad2d0504ebf6ca9ee638feb4b9cbb70c2"
            }
          ],
          "repo": "https://github.com/kazuph/mcp-fetch",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
      "CWE-918"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80347.json"
  },
  "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.",
  "id": "CVE-2026-80347",
  "modified": "2026-08-28T11:30:55.408427068Z",
  "published": "2026-08-26T10:09:47.977Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://www.npmjs.com/package/@kazuph/mcp-fetch"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80347.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80347"
    },
    {
      "type": "ADVISORY",
      "url": "https://www.vulncheck.com/advisories/mcp-fetch-through-1.6.3-server-side-request-forgery-via-unstripped-ipv6-literal-brackets"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/kazuph/mcp-fetch/issues/16"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/kazuph/mcp-fetch"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "mcp-fetch through 1.6.3 Server-Side Request Forgery via Unstripped IPv6 Literal Brackets"
}