Description
Mailpit's IsInternalIP deny list function fails to block the Azure WireServer address 168.63.129.16 and the RFC 2765/6145 IPv4-translated IPv6 prefix, allowing server-side request forgery to internal destinations. Attackers can supply hostnames resolving to these addresses in message content to reach the link check API and proxy endpoint for accessing internal resources.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| axllent | mailpit | ≤ 1.31.0 | — |
Advisories 1
- WID-SEC-2026-3138 MailPit: Schwachstelle ermöglicht Offenlegung von Informationen BSI CERT-Bund (WID) · Sep 1, 2026
References
- https://github.com/axllent/mailpit product
- Patch Commit patch
- https://github.com/axllent/mailpit/blob/v1.31.0/internal/tools/net.go technical-description
- VulnCheck Advisory: Mailpit SSRF Deny List Bypass via Azure Metadata and IPv6 Prefix third-party-advisory