CVE-2026-21859

Mailpit Proxy Endpoint is Vulnerable to Server-Side Request Forgery (SSRF)

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

axllent · mailpit

CVSS v3.1 NVD

5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS v3.1 GITHUB

5.8 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N

EPSS

0.81% chance of exploitation in the next 30 days, 56th percentile

Nuclei

high · CWE-918

Published

2026-01-07

Updated

2026-01-08

Proof-of-concept exploits (1)

• advisories/GHSA-8v65-47jx-7mfr

Nuclei templates (1)

• projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-21859.yaml

Security advisories

• axllent/mailpit/security/advisories/GHSA-8v65-47jx-7mfr
• axllent/mailpit/commit/3b9b470c093b3d20b7d751722c1c24f3eed2e19d

References

• CVE Record
• NVD entry