What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-20 · updated 2026-10-24
• Weakness: CWE-362

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 products

• axllent mailpit: before 1.30.0 — fixed in 1.30.0

How to fix

Upgrade to a fixed version: axllent mailpit 1.30.0. Check the vendor advisory for mitigations.

References

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

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