> ## Documentation Index
> Fetch the complete documentation index at: https://developer.upsun.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Composer 2.9 lands on Upsun PHP Images: Here’s what you need to know

> Remote code execution vulnerability in Next.js 15.x and 16.x App Router requires immediate patching. Learn how to secure your applications.

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<PostMeta data={{ author: ["thomasdiluccio"], date: "2025-12-25T11:00:00.000Z", image: "/images/posts/releases/composer-2.9/composer-2.9.webp" }} />

[Composer](https://getcomposer.org/) just shipped one of its most meaningful improvements in years: **automatic blocking of insecure and vulnerable PHP dependencies**.

This is great news for the PHP ecosystem. It’s also something you’ll want to understand before your next deploy suddenly stops mid-build, shouting about abandoned packages you forgot existed. (It happens to the best of us.)

Here’s the full breakdown.

## **What Changed in Composer 2.9?**

Composer 2.9 introduces [**Automatic Security Blocking**](https://blog.packagist.com/composer-2-9/). When installing without a `composer.lock` file, or updating dependencies, Composer now:

* Fails the build if a dependency has a known security advisory
* Can fail if a dependency is abandoned (optional, but available … and recommended)
* Provides a clear audit report of what’s wrong

This behaviour is **on by default**. Upsun doesn’t override it, because it makes everyone safer.

## **“But I didn’t change my dependencies… why is my build failing now?”**

Two reasons:

### 1. Your config file requires Composer 2 latest version.

A rebuild may pick up the latest version of Composer even if you’re still on the same PHP version. Boom: your dependencies are audited automatically. And, that’s great news!

### 2. Vulnerabilities are published continuously

Your dependencies might have been “fine” yesterday but vulnerable today. Composer 2.9 is simply letting you know about problems that already existed.

## **Why we ship Composer 2.9 as-is**

Short answer: because it’s good for you.

Longer answer:

* It prevents vulnerable or abandoned packages from silently entering your production chain.
* It pushes the ecosystem toward more secure baselines.
* Many users *want* this protection; they rely on it.

So instead of turning the feature off, we’re giving you the tools to use it effectively.

## **Your options if your build fails**

Let’s be straight: **The best fix is to patch or upgrade the affected dependencies.**

This is the healthiest thing you can do for your codebase, your users, and your future self. But you do have escape hatches.

### 1. Ignore specific advisories

```yaml {filename=".upsun/config.yaml (Upsun Flex) or .platform.app.yaml (Upsun Fixed)"} theme={null}
dependencies:
  php:
    config:
      audit:
        ignore:
          - "PKSA-yhcn-xrg3-68b1"
          - "PKSA-2wrf-1mxk-1pky"
```

### 2. Disable automatic blocking (not recommended, but available)

```yaml {filename=".upsun/config.yaml (Upsun Flex) or .platform.app.yaml (Upsun Fixed)"} theme={null}
dependencies:
  php:
    config:
      audit:
        block-insecure: false
```

### 3. Ignore vulnerabilities based on their severity rating (low/medium/high)

```yaml {filename=".upsun/config.yaml (Upsun Flex) or .platform.app.yaml (Upsun Fixed)"} theme={null}
dependencies:
  php:
    config:
      audit:
        ignore-severity:
           low:
             apply: all <-- ignore all low severity findings
```

## How Upsun handles Composer

A common question is whether you can revert to an older Composer version to avoid these checks.

### The Build process “catch-22”

Every Upsun PHP image includes a pre-installed, global Composer binary. Currently, this is version 2.9 or newer, which orchestrates your entire build:

* The pre-installed global binary (always the latest Composer version available) is what initiates your build process.
* Because this global binary is version 2.9+, it automatically performs a security audit before executing any other commands.
* Even if you specify an older Composer version in your dependencies block, that version is installed by the global 2.9 binary.
* The result: The security audit triggers and fails the build before your requested older version is even downloaded.

### The Solution

Since you cannot bypass the global binary, you should not attempt to downgrade the tool. Instead, use the `audit` configuration to ignore specific IDs or severities.
The most robust long-term solution remains keeping your dependencies updated and secure.

## **A gentle nudge: Keep those dependencies fresh**

Security blocking may feel strict at first, but here’s the upside:

* You learn about vulnerabilities early, before they sneak into production.
* Your app becomes more resilient.
* Your future upgrades stop being archaeology expeditions.

In other words: **modernizing your dependencies regularly is now a power move, not a chore**.

Composer 2.9 also allows you to block abandoned packages. Go the extra mile and secure your PHP apps' future.

```yaml {filename=".upsun/config.yaml (Upsun Flex) or .platform.app.yaml (Upsun Fixed)"} theme={null}
dependencies:
  php:
    config:
      audit:
        block-insecure: true
        block-abandoned: true
```

## **What you should do today**

* Run `composer audit` locally to see what’s coming.
* Review your project’s dependency tree (yes, even the old stuff).
* Decide whether to upgrade, ignore advisories, or temporarily opt out.

And remember: your next deployment might use Composer 2.9 unless you pin it explicitly.

## **If you need help, we’re here!**

Hit us up on [Discord](https://discord.gg/upsun) or open a [support ticket](https://docs.upsun.com/learn/overview/get-support.html). We want this transition to be smooth, and this feature actually makes your apps safer and easier to maintain in the long term.

And hey: if this blog post saved you an afternoon of head-scratching, go upgrade a dependency today. Your future deployments will thank you.