CVE-2026-55187CWE-918

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

Medium · published July 10, 2026

CVSS v3.1
5.8
EPSS
0%
Percentile
31.3
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
5.8 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00384 · 31.3th percentile
Weakness
CWE-918 · Server-Side Request Forgery (SSRF)
Published
2026-07-10T21:43Z
EPSS history
Timeline
  • 10 JUL 21:43Z
    Mailpit: Incomplete SSRF protection in Link Check API via IPv6 transition mechanisms (follow-up to CVE-2026-27808)
    cvelistv5