CVE-2026-118538: a2ui legacy Lit renderer uncontrolled property injection

CVE-2026-118538 · Severity: medium · CVSS 5.5 · Published 2026-10-28

a2ui is a web UI framework library used to render components on web pages. A vulnerability in its legacy 0.8 renderer allows a server to inject arbitrary HTML or JavaScript code by setting element properties that should be restricted, such as innerHTML or event handlers. An attacker who controls the server can achieve HTML injection and script execution on client browsers when a developer has opted in to use custom elements.

Technologies: A2ui-Project A2ui. Vendors: A2ui-Project.

Quick answers

Is CVE-2026-118538 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-118538 being exploited in the wild.
How severe is CVE-2026-118538?
Medium severity, with a CVSS score of 5.5, published 28 October 2026.
Which products and versions are affected?
A2ui-Project A2ui up to 0.12.0.
Is there a fix for CVE-2026-118538?
No fixed version is recorded yet. Disable custom elements rendering by setting enableCustomElements to false unless absolutely required. Alternatively, restrict the spread of server-controlled properties to an explicit allowlist excluding innerHTML, outerHTML, srcdoc, is, formaction, href, src, on* event handlers, style, and data-* attributes. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-118538 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-118538?
Check whether you run A2ui-Project A2ui 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.

How to fix

Disable custom elements rendering by setting enableCustomElements to false unless absolutely required. Alternatively, restrict the spread of server-controlled properties to an explicit allowlist excluding innerHTML, outerHTML, srcdoc, is, formaction, href, src, on* event handlers, style, and data-* attributes.

Technical details

The vulnerability exists in Root.renderComponentTree (src/0.8/ui/root.js, lines 211–215 and 544–548) where server-supplied property names are spread directly onto DOM elements without allowlisting: `el[prop] = val`. This reaches dangerous sinks like innerHTML, outerHTML, src, href, srcdoc, is, and formaction. The attack requires the opt-in developer flag enableCustomElements to be true and an application-registered custom element that preserves its light DOM; exploitation grants XSS-class capabilities.

Affected products

  • a2ui-project a2ui up to 0.12.0

Timeline

  • 2026-10-28: disclosed: CVE-2026-118538 published
  • 2026-10-08: other: Issue #3076 opened on GitHub

References

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