go-mail has insufficient address encoding when passing mail addresses to the SMTP client

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2025-59937: 0.54% estimated exploitation activity in the next 30 days; percentile 45.59 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Due to incorrect handling of the mail.Address values when a sender- or recipient address is passed to the corresponding MAIL FROM or RCPT TO commands of the SMTP client, this could lead to a possible wrong address routing or even to ESMTP parameter smuggling. Vulnerability details Instead of making use of the String() method of mail.Address, which takes care of proper escaping and quotation of mail address, we used the Address value of the mail.Address which is the raw value when passing it to our SMTP client. This meant, if a mail address like this was set: "toni.tester@example.com ORCPT=admin@admin.com"@example.com for a sender or recipient, instead of the correctly quoted/escaped address, the SMTP client would get the raw value passed which would translate into something like this being passed to the SMTP server: RCPT TO:<toni.tester@example.com ORCPT=admin@admin.com@example.com. Since ORCTP is a valid command for the SMTP server, the mail would be routed to the wrong…

Published by the source

29 Sep 2025, 16:28 UTC

Last modified by the source

5 Nov 2025, 22:02 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-wpwj-69cm-q9c5

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# Patch Next advisory brief: CVE-2025-59937

Advisory: go-mail has insufficient address encoding when passing mail addresses to the SMTP client
IDs: CVE-2025-59937, GHSA-wpwj-69cm-q9c5
Record: https://patchnext.com/advisories/cve-2025-59937 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/wneessen/go-mail 0.7.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/wneessen/go-mail: affected < 0.7.1; fixed in 0.7.1

## Suggested inspection (read-only)
- Go github.com/wneessen/go-mail: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/wneessen/go-mail.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-wpwj-69cm-q9c5 (GitHub-reviewed advisory GHSA-wpwj-69cm-q9c5 lists affected ranges: Go github.com/wneessen/go-mail >=0 <0.7.1)

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