How severe is CVE-2025-59937?

No CVSS score has been assigned to CVE-2025-59937 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2025-59937?

CVE-2025-59937 affects the following packages: github.com/wneessen/go-mail (Go). Ecosystems affected: Go.

How do I fix CVE-2025-59937?

Update github.com/wneessen/go-mail to 0.7.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-59937 is resolved across your whole dependency graph.

How do I detect CVE-2025-59937 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/wneessen/go-mail, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2025-59937 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2025-59937 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-59937 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-59937?

CVE-2025-59937 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 46th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2025-59937?

CVE-2025-59937 is classified as CWE-88 (CWE-88). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-59937 published, and has it been updated?

CVE-2025-59937 was published on September 29, 2025 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

CVE-2025-59937 — go-mail

Fix: wneessen/go-mail@42e92cf

CVE-2025-59937 is a CWE-88 vulnerability in github.com/wneessen/go-mail. A fix is available for github.com/wneessen/go-mail — see the affected versions and patch details below.

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

Also known asGHSA-wpwj-69cm-q9c5GO-2025-3988

Published

Sep 29, 2025

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-59937.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs46th percentile — riskier than 46% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐹github.com/wneessen/go-mail

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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: "[email protected]> [email protected]"@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:<[email protected]> [email protected]@example.com>.

Since ORCTP is a valid command for the SMTP server, the mail would be routed to the wrong address. Additionally, other SMTP commands could potientially be smuggled in using this method causing unexpected behaviour.

Exploitation requirements

For successful exploitation of this vulnerability it is required that the user's code is allowing for arbitrary mail address input (i. e. through a web form or similar). If only static mail addresses are used (i. e. in a config file) and the mail addresses in use do not consist of quoted local parts, this should not affect your code.

Patches

The vulnerability has been fixed with PR #496 and the fix has been shipped with the go-mail v0.7.1 release.

Issue #495 holds the full report and discussion.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/wneessen/go-mail`	all versions	0.7.1`go get github.com/wneessen/go-mail@v0.7.1`

Affected Products

1 product · 1 configurations

Application

go-mailpebcak

< 0.7.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/wneessen/go-mail, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/wneessen/go-mail to 0.7.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-59937 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### 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: `"t

O3 Security · Impact-Aware SCA

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