CVE-2026-118273

A2UI sparse-array updates can exhaust renderer memory

a2ui-project · A2UI @a2ui/web_core data model

First documented disclosure · Review checkpoint

Summary

A crafted data-model update with an extreme array index can hang or crash the UI renderer.

Severity and exploitation evidence

Medium · 5.3/10 · CVSS 4.0. Severity source.

Exploitation not established: The reviewed primary sources establish a vulnerability and controlled reproduction, not real-world malicious exploitation. CISA KEV 2026.10.27 contains no exact-ID match; absence is not proof of no exploitation.

Technical severity is not a measure of observed attacks or of risk to your deployment. Attempts, demonstrations, and successful compromise retain the qualifications in the source.

How the weakness works

DataModel.set grows a sparse array without an index bound; an ancestor-bound signal then spreads its entire logical length into a dense copy.

Conditions required

Ability to supply an update to the affected renderer with a signal bound to the relevant array; CNA rates low privileges and no user interaction.

Potential impact

Client availability loss through excessive allocation; confidentiality or integrity impact is not established.

Affected versions and configurations

CNA lists 0.10.0–0.10.6; researcher reproduced published @a2ui/web_core 0.10.6.

Fix and mitigation status

Fixed by commit 82789191ce551f4d7a095d273773fb24bd764c9d, merged September14. A containing published package version was not verified.

Practical next steps

Apply the confirmed index-bound/safe-cloning fix or use a release verified to contain it; bound message indices and resource use before rendering.

Operating lesson

Validate the resource cost of agent-generated UI data, not only its syntax.

Evidence and limits

August25 public issue and September14 merge predate October28 CVE. The maintainer reproduced the resource-exhaustion mechanism; demonstration is not evidence of malicious use.

Sources