# 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.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Aug 2026
- **Updated:** 21 Aug 2026
- **Also known as:** GHSA-w878-pj84-3j5v, GO-2026-6363

## 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 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-67445?

3 open source packages ship an affected version, including github.com/axllent/mailpit.


| Package | Ecosystem | 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.

## Is CVE-2026-67445 being exploited?

There is no known exploitation of CVE-2026-67445 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-67445 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-67445 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/axllent/mailpit (Go): affected all versions; fixed in 1.30.4
- github.com/axllent/mailpit (Go): affected all versions; fixed in 1.30.4
- github.com/axllent/mailpit (Go): affected all versions; fixed in 1.30.4

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-67445/ (Markdown: https://insights.sbomify.com/CVE-2026-67445/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-67445
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-67445
- OSV: https://osv.dev/vulnerability/CVE-2026-67445

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-67445/
Summaries are generated and may contain mistakes; the official description above is the record.