What is CVE-2026-21859?

CVE-2026-21859 is a medium-severity vulnerability in Axllent Mailpit, classified under Server-Side Request Forgery (SSRF). CVSS score: 5.8/10. Published 2026-01-08.

How severe is CVE-2026-21859?

Medium severity. CVSS v3 base score is 5.8 out of 10.

SSRF in Axllent Mailpit

CVE-2026-21859

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.

Vulnerability class: SSRF (Server-Side Request Forgery)

EPSS: 0.008 (53.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.8 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N.

Affected products

Axllent Mailpit — versions < 1.28.1

Weakness classification (CWE)

CWE-918 — Server-Side Request Forgery (SSRF)

References

security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)

Frequently asked questions

What is CVE-2026-21859?: CVE-2026-21859 is a medium-severity vulnerability in Axllent Mailpit, classified under Server-Side Request Forgery (SSRF). CVSS score: 5.8/10. Published 2026-01-08.
How severe is CVE-2026-21859?: Medium severity. CVSS v3 base score is 5.8 out of 10.