CVE-2026-79319: Stencil Core Authentication Bypass Flaw

CVE-2026-79319 Overview

CVE-2026-79319 affects Stencil core version 4.43.5, a toolchain for building reusable, scalable web component libraries. The vulnerability is classified as Incorrect Access Control, indicating that the framework does not properly enforce authorization boundaries in the affected release. Applications built with this version of Stencil may expose functionality or data intended to be restricted. Public details are hosted in a third-party research repository, and no vendor advisory has been issued at the time of publication.

Critical Impact
An Incorrect Access Control weakness in Stencil core 4.43.5 can allow unauthorized actors to bypass intended permission checks in downstream web component applications.

Affected Products

Stencil core 4.43.5
Web component libraries and applications built on the affected Stencil release
Downstream projects consuming the vulnerable @stencil/core package version

Discovery Timeline

2026-09-21 - CVE-2026-79319 published to the National Vulnerability Database (NVD)
2026-09-22 - Last updated in the NVD database

Technical Details for CVE-2026-79319

Vulnerability Analysis

CVE-2026-79319 is an Incorrect Access Control issue in Stencil core 4.43.5. Stencil is an open-source compiler that generates standards-based web components used in production sites and design systems. The public CVE record states that the affected version fails to enforce access restrictions correctly, without specifying the affected API surface. Because Stencil compiles output shipped to browsers and node-based tooling, a permissions gap in the framework can propagate to every application consuming the vulnerable release. Downstream impact depends on which framework component enforces the missing check and how consuming applications rely on it. Technical particulars, including exploitation preconditions and affected code paths, are documented in the referenced GitHub CVE-2026-79319 Details writeup.

Root Cause

The root cause is an authorization control that is missing, incomplete, or incorrectly evaluated within @stencil/core 4.43.5. Incorrect Access Control weaknesses typically arise when a code path assumes trust from an upstream caller, when a check is applied inconsistently across entry points, or when a privileged operation is exposed without a guarding predicate. The upstream project source is available in the GitHub StencilJS Core Repository for maintainers reviewing the affected logic.

Attack Vector

The attack vector is not specified in the published CVE record. Incorrect Access Control flaws in a compiler and runtime library such as Stencil generally require an attacker to interact with an application built on the vulnerable version, either through crafted requests or by invoking an exposed function that lacks a proper authorization check. Confirmed exploitation details, proof-of-concept code, and prerequisites should be validated against the third-party research writeup before drawing operational conclusions.

No verified proof-of-concept code has been published for CVE-2026-79319 at the time of writing. Refer to the linked research repository for any subsequently released technical detail.

Detection Methods for CVE-2026-79319

Indicators of Compromise

Unexpected access to routes, components, or APIs in Stencil-based applications that should be gated by authorization.
Application logs showing successful requests to privileged handlers without preceding authentication events.
Anomalous invocation of internal component methods from untrusted client contexts.

Detection Strategies

Perform a software composition analysis (SCA) scan across build manifests to identify projects pinning @stencil/core at version 4.43.5.
Review authorization test coverage for components and routes generated by Stencil to confirm access checks execute as intended.
Correlate web server and application telemetry to identify requests that bypass expected authentication flows.

Monitoring Recommendations

Alert on package installations or CI builds that resolve @stencil/core to the affected 4.43.5 release.
Monitor egress and privileged endpoint access patterns for Stencil-based frontends and their backing APIs.
Track advisory updates on the StencilJS Core Repository for a fixed release and backported patches.

How to Mitigate CVE-2026-79319

Immediate Actions Required

Inventory all applications and libraries that depend on @stencil/core 4.43.5.
Restrict exposure of Stencil-built applications behind authenticated reverse proxies or API gateways until a patch is validated.
Add server-side authorization enforcement for any operation that currently relies on client-side or framework-level checks.

Patch Information

No vendor advisory or fixed version is listed in the NVD record for CVE-2026-79319 at the time of publication. Consumers should track the StencilJS Core Repository releases and upgrade to a version later than 4.43.5 once the maintainers publish a fix that references this CVE.

Workarounds

Downgrade to a prior Stencil release that predates the introduction of the vulnerable behavior after regression testing.
Implement compensating server-side access control checks so that authorization does not depend solely on framework-generated logic.
Limit network reachability of Stencil-based administrative interfaces to trusted networks and identities.

bash

# Identify projects using the affected Stencil core version
npm ls @stencil/core | grep 4.43.5

# Pin to a non-affected version once a fixed release is published
npm install @stencil/core@latest --save-exact