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

Source

https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-21859.yaml

Associated Vulnerability

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

Description

Mailpit <= 1.28.0 contains a server-side request forgery caused by insufficient validation of internal IP addresses in the /proxy endpoint, letting attackers make requests to internal network resources, exploit requires crafted HTTP GET requests.

File Snapshot

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