Mailpit SSRF Deny List Bypass via Azure Metadata and IPv6 Prefix

Advisories

Mailpit SSRF Deny List Bypass via Azure Metadata and IPv6 Prefix

severity: medium
date: 9/1/2026
Affecting: mailpit <= 1.31.0
CVE: CVE-2026-84697
CWE: CWE-918 Server-Side Request Forgery (SSRF)
CVSS: 6.9
CVSS V4 Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
References: https://github.com/axllent/mailpit
Patch Commit
https://github.com/axllent/mailpit/blob/v1.31.0/internal/tools/net.go
Credit: euriconicacio
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.

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