# CVE-2026-67447: Mailpit: SMTP DATA line reader buffers over-limit input before size enforcement

> Unauthenticated attackers can cause memory exhaustion in Mailpit by sending oversized SMTP DATA lines before size limits are enforced.

- **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-r553-m4fv-5v97, GO-2026-6272

## What is CVE-2026-67447?

CVE-2026-67447 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. From 1.30.0 until 1.30.5, Mailpit's internal/smtpd/smtpd.go readData() function calls bufio.Reader.ReadBytes before applying the len(data)+len(line) size check to the completed SMTP DATA line against Server.MaxSize. An unauthenticated SMTP client can send a single line larger than the configured MaxMessageSize, causing the full line to be allocated before Mailpit returns the 552 5.3.4 rejection. This post-fix gap remains after normal multi-line DATA accumulation was bounded, and concurrent oversized lines can create substantial memory pressure beyond the configured message-size cap. This issue is fixed in version 1.30.5.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-67447?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/axllent/mailpit` | Go | From 1.30.0 | 1.30.5 |
| `github.com/axllent/mailpit` | Go | From 1.30.0 | 1.30.5 |
| `github.com/axllent/mailpit` | Go | From 1.30.0 | 1.30.5 |

## How do I fix CVE-2026-67447?

Upgrade github.com/axllent/mailpit to 1.30.5 or later.

## Is CVE-2026-67447 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-67447 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-67447 and fix it if it is affected.

What it is: CVE-2026-67447 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-67447 exists.

Affected packages and fixed versions:
- github.com/axllent/mailpit (Go): affected from 1.30.0; fixed in 1.30.5
- github.com/axllent/mailpit (Go): affected from 1.30.0; fixed in 1.30.5
- github.com/axllent/mailpit (Go): affected from 1.30.0; fixed in 1.30.5

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-2026-67447/ (Markdown: https://insights.sbomify.com/CVE-2026-67447/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-67447
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-67447
- OSV: https://osv.dev/vulnerability/CVE-2026-67447

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-67447/
Summaries are generated and may contain mistakes; the official description above is the record.