CVE-2026-80347

Name of the Vulnerable Software and Affected Versions mcp-fetch (affected versions not specified)

Description The software fails to remove brackets surrounding an IPv6 literal when validating a fetch target against its Server-Side Request Forgery (SSRF) guard. The isSafeUrl function extracts the hostname from the parsed URL, but for literals like http://[::1]/, it retains the brackets. When this bracketed string is passed to net.isIP, the function returns zero, causing the system to skip private-address checks. Since the bracketed string is not a resolvable name, the guard incorrectly reports the target as safe. The HTTP client subsequently strips the brackets and establishes a connection. This allows access to any IPv4 target, including link-local metadata endpoints, especially when addresses are provided in IPv4-mapped form. Additionally, the isPrivateIPv6() function does not account for the ::ffff: prefix, allowing mapped forms to bypass checks. An attacker capable of influencing the model's requests can use this to read internal responses back into the model context.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.