CVE-2026-45712 Mailpit: Concurrent map read & write in proxy CSS rewriter - remote unauth crash (fatal error: concurrent map read and map write)
Unauthenticated remote attackers can crash the Mailpit server via a race condition in the proxy CSS rewriter, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45712?
CVE-2026-45712 is a medium-severity vulnerability in axllent mailpit, published on 20 Jul 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 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.
Which versions are affected by CVE-2026-45712?
3 open source packages ship an affected version, including github.com/axllent/mailpit. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/axllent/mailpit Go | All versions | 1.30.0 |
github.com/axllent/mailpit Go | All versions | 1.30.0 |
github.com/axllent/mailpit Go | All versions | 1.30.0 |
Products include Axllent Mailpit.
How do I fix CVE-2026-45712?
Upgrade github.com/axllent/mailpit to 1.30.0 or later.
Is CVE-2026-45712 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-45712 exists.
Other vulnerabilities in axllent mailpit
- CVE-2026-45713 Mailpit: Unauthenticated remote memory-exhaustion DoS via unlimited SMTP DATA and /api/v1/send body sizes
- CVE-2026-22689 Mailpit is vulnerable to Cross-Site WebSocket Hijacking (CSWSH) allowing unauthenticated access to emails
- CVE-2026-45711 Mailpit: Path traversal & arbitrary file write in mailpit dump --http via attacker-controlled message IDs
- CVE-2026-45709 Mailpit has an incomplete fix for GHSA-6jxm: HTML check still permits SSRF to private/loopback/IMDS via missing IP-filter dialer
- CVE-2026-27808 Mailpit is Vulnerable to Server-Side Request Forgery (SSRF) via Link Check API
Sources
Also known as GHSA-w4vj-r5pg-3722, GO-2026-5689.