Is CVE-2026-43981 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-43981 being exploited in the wild.

How severe is CVE-2026-43981?

Informational severity, with a CVSS score of 8.2, published 26 May 2026.

Is there a fix for CVE-2026-43981?

A patch was published on 2026-05-26: Fix released in version 1.17.6 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-43981 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-43981?

Check whether you run Xyproto Algernon at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-43981: xyproto Algernon race condition in Lua handler

CVE-2026-43981 · Severity: info · CVSS 8.2 · Published 2026-05-26

Algernon is a standalone web server that allows developers to use the Lua programming language for web logic. A flaw in how the server handles multiple simultaneous requests can lead to internal memory corruption within its Lua engine. In practice, an attacker or even heavy legitimate traffic can cause the web server to crash or behave unpredictably, resulting in a denial of service.

Technologies: Xyproto Algernon. Vendors: Xyproto.

Quick answers

Is CVE-2026-43981 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-43981 being exploited in the wild.
How severe is CVE-2026-43981?: Informational severity, with a CVSS score of 8.2, published 26 May 2026.
Which products and versions are affected?: Xyproto Algernon < 1.17.6.
Is there a fix for CVE-2026-43981?: A patch was published on 2026-05-26: Fix released in version 1.17.6 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-43981 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-43981?: Check whether you run Xyproto Algernon at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A race condition exists in 'engine/luahandler.go' due to improper synchronization of the gopher-lua LState. The 'sync.RWMutex' protecting 'LoadCommonFunctions' is released prematurely before 'L.Push()' and 'L.PCall()' are executed. Because the underlying Lua state is not thread-safe, concurrent network requests can access the shared state simultaneously, leading to Lua VM corruption. This vulnerability allows a remote attacker to trigger a denial of service (DoS) by sending concurrent requests. The issue is resolved in version 1.17.6.

Affected products

xyproto Algernon < 1.17.6

Timeline

2026-04-19: disclosed: Initial report to maintainer
2026-05-05: advisory: GitHub Security Advisory published
2026-05-26: patched: Fix released in version 1.17.6

References

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