CVE-2026-21859: Mailpit Proxy Endpoint is Vulnerable to Server-Side Request Forgery (SSRF)

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-01-08 · updated 2026-06-17
Weakness: CWE-918

Description

Mailpit is an email testing tool and API for developers. Versions 1.28.0 and below have a Server-Side Request Forgery (SSRF) vulnerability in the /proxy endpoint, allowing attackers to make requests to internal network resources. The /proxy endpoint validates http:// and https:// schemes, but it does not block internal IP addresses, enabling attackers to access internal services and APIs. This vulnerability is limited to HTTP GET requests with minimal headers. The issue is fixed in version 1.28.1.

Affected products

axllent mailpit: before 1.28.1 — fixed in 1.28.1

How to fix

Upgrade to a fixed version: axllent mailpit 1.28.1. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-21859 or the next vulnerability affects your stack