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CVE-2026-80347: mcp-fetch

Severity

8.7 (HIGH)

Vendor

KAZUPH

Affected versions

0 through 1.6.3

Patch status

Unknown

Published

2026-08-26T10:16:42.803

Modified

2026-08-26T13:19:24.960

Why it matters

High-severity vulnerability requiring prioritized review.

Recommended admin actions

• Review and patch based on exposure, asset criticality, and business impact.

Technical 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, 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.

View the official NVD record for CVE-2026-80347

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.