What’s Vulnerable › Vulnerabilities

CVE-2026-55187: Mailpit: Incomplete SSRF protection in Link Check API via IPv6 transition mechanisms (follow-up to CVE-2026-27808)

• Severity: medium (CVSS 5.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-10 · updated 2026-10-25
• Weakness: CWE-918

Description

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

References

• https://github.com/axllent/mailpit/commit/a88dadbbe1df016a35a445089ef2a362a6c2de78
• https://github.com/axllent/mailpit/releases/tag/v1.30.2
• https://github.com/axllent/mailpit/security/advisories/GHSA-w4mc-hhc6-xp28
• https://github.com/axllent/mailpit/security/advisories/GHSA-w4mc-hhc6-xp28

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