CVE-2026-43981
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAlgernon 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA race condition exists in Algernon's Lua handler where a sync.RWMutex protecting LoadCommonFunctions is released before L.Push() and L.PCall() complete. Since gopher-lua's LState is explicitly not goroutine-safe, concurrent HTTP requests race on the shared Lua VM state, causing memory corruption and potential crashes.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- Authentication
- X
- User interaction
- None
- Scope
- X
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Algernon installation and versionRun 'algernon --version' or check the binary version. If using a package manager, check 'algernon -v' or your package manager's version query.Affected if The installed version is earlier than 1.17.6 (versions 1.17.0 through 1.17.5 are affected).
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Determine if Lua script execution is enabledReview your Algernon configuration files (algernon.conf, config.lua, or command-line flags) for Lua module loading or script execution settings. Look for 'lua', 'module', or 'preload' directives.Affected if Lua execution is enabled and the server handles concurrent HTTP requests that trigger Lua scripts via LoadCommonFunctions.
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Check for concurrent request handlingExamine your deployment to see if Algernon is configured to handle multiple concurrent requests (the default mode). This is typically the case for any production deployment.Affected if Multiple concurrent requests can be processed simultaneously, which enables the race condition on the shared LState.
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Look for race condition symptomsRun Algernon with the Go race detector enabled (GODEBUG=race=1) under concurrent load. Monitor for crashes, panic messages mentioning 'fault' or 'unexpected', or Lua VM errors.Affected if The program exhibits VM corruption, crashes, or race detector warnings when under concurrent Lua request load.
You are affected if Algernon versions before 1.17.6 are running with concurrent Lua script execution enabled, and you observe race-related crashes or corruption under load.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade to Algernon version 1.17.6 or later, which contains the fix for proper mutex synchronization around Lua state operations.
1.17.6
- Upgrade Algernon to version 1.17.6 or later
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation1.0 h
- Testing3.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-43981 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-43981 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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