CVE-2026-43981: Xyproto Algernon

High severity, CVSS 8.2. EPSS: 0.3% chance of exploitation in the next 30 days.

Algernon is a small self-contained pure-Go web server. Prior to 1.17.6, in engine/luahandler.go, the sync.RWMutex protecting LoadCommonFunctions is released before L.Push() and L.PCall() execute. Since gopher-lua's LState is explicitly not goroutine-safe, concurrent requests race on the shared state causing Lua VM corruption. The Go race detector confirms this immediately under modest concurrency (ab -n 1000 -c 100). This vulnerability is fixed in 1.17.6.

Affected products

• Xyproto Algernon: before 1.17.6 (fixed in 1.17.6)

Published 2026-05-26. Last modified 2026-07-24.