CVE-2026-45712 is a medium-severity race condition vulnerability in github.com/axllent/mailpit (go), affecting versions < 1.30.0. It is fixed in 1.30.0.
Summary 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. Details A remote, unauthenticated attacker who can (1) reach /proxy and (2) plant any message with a stylesheet link in the inbox can crash Mailpit by issuing concurrent /proxy?data=… requests against the same message's CSS URL. Mailpit's defaults make both prerequisites trivial: the SMTP listener accepts mail anonymously, the HTTP listener accepts requests anonymously, and the cleanup goroutine fires every minute regardless of whether the map is being read. Affected code server/handlers/proxy.go:198-229 server/handlers/proxy.go:52-66 server/handlers/proxy.go:244-313 Go's map runtime sets a hashWriting flag at the start of any write op. Concurrent map reads check the flag and call throw("concurrent map read and map write"), throw is not caught by defer recover and is not caught by http.Server's handler-panic guard. The process exits with a stack trace. PoC Deposit any message with a <link rel="stylesheet" href="https://attacker.example/big.css"> in the store (SMTP or /api/v1/send, both unauthenticated by default). Make a few hundred concurrent requests to /proxy?data=base64(<id>:https://attacker.example/big.css), the attacker's big.css should be ~50 MiB and contain thousands of url(...) entries so each request spends time iterating the rewriter loop and touching assets[id] repeatedly. Skeleton (set --allow-internal-http-requests only if you're testing locally, internal IPs are blocked by safeDialContext in production, which is correct): When the unlocked read at line 216 happens during a delete() from the cleanup goroutine, or during another goroutine's assets[id] = result write, Go's runtime emits: …and the process exits. Building Mailpit with go build -race produces a deterministic WARNING: DATA RACE trace at the same line under the same workload, confirming the access pattern is racy even without timing-based crash demonstration. Impact Unauthenticated remote attacker can trigger a concurrent map access crash in /proxy, causing a fatal runtime panic and full Mailpit process termination (DoS).
Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing. Typical impact: TOCTOU exploits, data corruption, or privilege escalation.
CVE-2026-45712 has a CVSS score of 5.9 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (1.30.0). Upgrading removes the vulnerable code path.
go
github.com/axllent/mailpit (< 1.30.0)github.com/axllent/mailpit → 1.30.0 (go)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter instead of chasing every advisory.
Kodem's runtime-powered SCA identifies whether CVE-2026-45712 is reachable in your applications. Explore open-source security for your team.
See if CVE-2026-45712 is reachable in your applications. Get a demo
Upgrade github.com/axllent/mailpit to 1.30.0 or later to resolve this vulnerability.
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-45712 is a medium-severity race condition vulnerability in github.com/axllent/mailpit (go), affecting versions < 1.30.0. It is fixed in 1.30.0. Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing.
CVE-2026-45712 has a CVSS score of 5.9 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
github.com/axllent/mailpit (go) versions < 1.30.0 is affected.
Yes. CVE-2026-45712 is fixed in 1.30.0. Upgrade to this version or later.
Whether CVE-2026-45712 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade github.com/axllent/mailpit to 1.30.0 or later.