CVE-2026-43981: Algernon: Race Condition in handle() shared LState

Severity: high (CVSS 8.2 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-26 · updated 2026-07-24
Weakness: CWE-362

Description

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

References

https://github.com/xyproto/algernon/issues/172
https://github.com/xyproto/algernon/security/advisories/GHSA-rr2f-4wrm-h6rg

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