Server builder assets can overwrite the generated main.js entry point

[BlueIridium]

Command

build, run

Is this a regression?

No. The server builder has copied configured assets after Webpack output since the assets option was released in 15.1.0.

The previous version in which this bug was not present was

No response.

Description

@angular-devkit/build-angular:server copies configured assets after Webpack emits the server program, without checking whether an asset destination is already a generated file.

With a recursive asset tree copied to output ., an asset named main.js silently replaces the generated server entry point. The build reports success, and normal node dist/server/main.js startup executes the asset instead of the generated application bundle.

I reproduced this with an asset-only dependency update. Version 1.0.0 contains only assets/data.json; version 1.0.1 adds only assets/main.js. Neither version declares scripts, main, exports, imports, or bin, installation uses --ignore-scripts, and the application never imports the package.

Expected: the build should reject an asset/generated-output collision, or keep generated output authoritative.

Actual: the build succeeds and the final dist/server/main.js is byte-for-byte identical to the dependency asset. Starting it executes dependency-controlled code as the deployed server process.

Minimal Reproduction

Repository: https://github.com/BlueIridium-Security/angular-server-asset-entry-collision-repro

git clone https://github.com/BlueIridium-Security/angular-server-asset-entry-collision-repro.git
cd angular-server-asset-entry-collision-repro
./scripts/validate.sh

The validator runs clean → attack → restored-clean → restored-attack. Across two fresh-container runs, clean 1.0.0 always emitted and started the same genuine 782,472-byte bundle with no marker; attack 1.0.1 always emitted the exact 192-byte package asset and executed its marker. Runtime networking is disabled, and the script fails on any control mismatch.

Exception or Error

No exception is reported. The builder reports successful bundle generation and asset copying.

Your Environment

Angular CLI: 22.2.0
@angular-devkit/build-angular: 22.2.0
Angular: 22.2.0
Node: 24.21.0
npm: 11.19.0
OS: Linux arm64 container (node:24.21.0-bookworm-slim)

Anything else relevant?

The builder is deprecated but remains shipped. The default server assets list is empty, and exploitation requires an opt-in recursive root-output rule plus an accepted package update, build, deployment, and startup. I therefore assess this as High rather than Critical.

Current source shows the server builder calling copyAssets() after successful Webpack output, while copyAssets() writes each destination without checking generated outputs.

This is distinct from #19157 and #16670, which discuss precedence between two configured asset inputs rather than a post-Webpack asset replacing the executable generated entry point.

Should the server builder reject configured asset destinations that collide with generated output files?

[alan-agius4]

Thank you for reporting.

This does not represent a valid security vulnerability or threat model:

1. Source code, configuration, and dependencies are trusted: Build tools operate under the assumption that the project configuration (angular.json), source files, and installed dependencies are within the trust boundary.
2. Expected behavior based on configuration: The project configuration explicitly instructs the builder to copy all files from the specified asset path into the root output directory (output: "."). The build copying an asset named main.js over the generated entry point is the direct result of this explicit user configuration.

Closing this issue as not a vulnerability and working as intended based on the provided configuration.