CVE-2026-67445 Mailpit: SMTP command parser buffers unbounded command lines before syntax rejection
Unauthenticated remote attackers can cause denial of service in Mailpit by sending oversized SMTP command lines that exhaust memory before validation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-67445?
CVE-2026-67445 is a medium-severity denial of service vulnerability in axllent mailpit, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Mailpit is an email testing tool and API for developers. Prior to 1.30.4, Mailpit reads SMTP commands through internal/smtpd/smtpd.go session.readLine() using bufio.Reader.ReadString before session.parseLine() parses the verb or the RFC 5321 512-octet command-line limit is enforced. An unauthenticated remote SMTP client can send an oversized single command line that is fully allocated before syntax rejection or timeout, and the normal MaxMessageSize and DATA limits do not apply to this pre-DATA path. The same command reader is used by handleAuthLogin(), handleAuthPlain(), and handleAuthCramMD5() continuation lines, so concurrent oversized inputs can create memory pressure and reduce service availability. This issue is fixed in version 1.30.4.
Weakness: CWE-400
Which versions are affected by CVE-2026-67445?
3 open source packages ship an affected version, including github.com/axllent/mailpit.
| Package | Affected | Fixed in |
|---|---|---|
github.com/axllent/mailpit Go | All versions | 1.30.4 |
github.com/axllent/mailpit Go | All versions | 1.30.4 |
github.com/axllent/mailpit Go | All versions | 1.30.4 |
How do I fix CVE-2026-67445?
Upgrade github.com/axllent/mailpit to 1.30.4 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-67445 being exploited?
There is no known exploitation of CVE-2026-67445 in the wild and no public exploit code.
Sources
Also known as GHSA-w878-pj84-3j5v, GO-2026-6363.