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Vulnerability · Published Jul 10, 2026 · Assigned by GitHub_M

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

Medium 5.8

In plain English

A medium-severity server-side request forgery in mailpit from axllent. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 29% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.8Medium
Exploit odds (30 days)0.4%top 70.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/axllent/mailpit1.30.2GO-2026-5688
Gogithub.com/axllent/mailpit1.30.2GHSA-w4mc-hhc6-xp28

Affected products (as reported)

VendorProductVersions
axllent mailpit < 1.30.2

Weakness: CWE-918 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N

References