CVE-2026-55187: Axllent Mailpit

Medium severity, CVSS 5.8. EPSS: 0.4% chance of exploitation in the next 30 days.

Mailpit is an email testing tool and API for developers. Prior to 1.30.2, the remediation shipped for CVE-2026-27808 is incomplete because the tools.IsInternalIP deny-list in internal/tools/net.go relies on Go's standard library classification helpers and does not block IPv6 transition mechanisms or prefixes such as NAT64, 6to4, IPv4-compatible IPv6, ISATAP, fec0::/10, and 2001:db8::/32. An attacker who can deliver email and invoke POST /api/v1/message/{ID}/link-check can coerce the Link Check API's safeDialContext path into dialing internal destinations and can use status-code and error feedback to map internal service reachability, including cloud metadata endpoints. This issue is fixed in version 1.30.2.

Affected products

• Axllent Mailpit: before 1.30.2 (fixed in 1.30.2)

Published 2026-07-10. Last modified 2026-07-13.