CVE-2026-55187
Mailpit: Incomplete SSRF protection in Link Check API via IPv6 transition mechanisms
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/axllent/mailpit | <= 1.30.1 | 1.30.2 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-w4mc-hhc6-xp28
- https://github.com/axllent/mailpit/security/advisories/GHSA-w4mc-hhc6-xp28
- https://nvd.nist.gov/vuln/detail/CVE-2026-55187
- https://github.com/axllent/mailpit/commit/a88dadbbe1df016a35a445089ef2a362a6c2de78
- https://github.com/axllent/mailpit/releases/tag/v1.30.2