Vulnerability · Published Aug 20, 2026 · Assigned by GitHub_M

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

Medium 5.3

In plain English

A medium-severity resource allocation without limits in mailpit from axllent. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.5%top 56.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/axllent/mailpit	1.30.5	GHSA-r553-m4fv-5v97
Go	github.com/axllent/mailpit	1.30.5	GO-2026-6272

Affected products (as reported)

Vendor	Product	Versions
axllent	mailpit	>= 1.30.0, < 1.30.5

Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

https://github.com/axllent/mailpit/security/advisories/GHSA-r553-m4fv-5v97 x_refsource_CONFIRM
https://github.com/axllent/mailpit/commit/8720c6bd8281fc00d458081908f1dbef8e59a98c x_refsource_MISC
https://github.com/axllent/mailpit/releases/tag/v1.30.5 x_refsource_MISC