Vulnerability · Published Jul 20, 2026 · Assigned by GitHub_M

CVE-2026-45712Mailpit: Concurrent map read & write in proxy CSS rewriter - remote unauth crash (fatal error: concurrent map read and map write)

Medium 5.9

In plain English

A medium-severity race condition in mailpit from axllent. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 27% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium

Exploit odds (30 days)0.3%top 72.9% 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. Prior to version 1.30.0, the screenshot/print proxy (/proxy?data=…) maintains a package-level assets map[string]MessageAssets cache, but reads the map without holding assetsMutex while a long-running cleanup goroutine and (re-entrant) CSS-rewriting code path concurrently write to it under the lock. When the unsynchronized read coincides with a synchronized write, Go's runtime raises fatal error: concurrent map read and map write — a runtime.throw that is not recoverable by http.Server's handler-panic recover. The whole Mailpit process exits, taking the SMTP, POP3 and HTTP listeners down with it. Version 1.30.0 contains a patch.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/axllent/mailpit	1.30.0	GO-2026-5689
Go	github.com/axllent/mailpit	1.30.0	GHSA-w4vj-r5pg-3722

Affected products (as reported)

Vendor	Product	Versions
axllent	mailpit	< 1.30.0

Weakness: CWE-362, CWE-770 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/axllent/mailpit/security/advisories/GHSA-w4vj-r5pg-3722 x_refsource_CONFIRM
https://github.com/axllent/mailpit/releases/tag/v1.30.0 x_refsource_MISC