Laravel 12.71 Brings the Concurrency Security Fix to Laravel 12

If your app runs on Laravel 12, there is one update worth doing today. Laravel 12.71.0, released on 3 November 2026, backports the security fix for the Concurrency facade that first landed in Laravel 13.40. It closes a hole where a task's own output could forge the result your app receives — and the fix needs no code changes from you at all.

The short version

• What: Laravel 12.71.0 fixes a result-injection flaw in Concurrency::run() when it uses the process driver.
• Who is affected: any Laravel 12 app that calls Concurrency::run() with the process driver (the default). If you never use Concurrency, this release changes nothing for you.
• What to do: run composer update laravel/framework and check that you are on 12.71.0. That is the whole fix.
• No code changes, no config changes. If you worked around the bug by switching tasks to the sync driver or stripping output from them, you can undo that workaround after updating.

What was actually wrong

Concurrency::run() lets you run several closures at the same time. With the process driver, Laravel serializes each closure, starts a child php artisan process for it, and reads the result back from that child's standard output. The parent then calls unserialize() on what it reads.

The problem is that everything a task prints goes to that same standard output. Up to version 12.70.x, the parent found the result by cutting the output at the first gzip marker bytes and decoding the JSON it found there. So a task that printed text an attacker controls could print a fake result — and your web process would happily unserialize it. In the lab, a task that printed a forged result and then returned 'real' came back as 'forged' on 12.70.1. That is a remote code execution flaw, not just a crash.

There was a second, everyday side to the same bug. Any plain echo inside a task — a progress line, a debug print — broke the result parsing, and the parent crashed with "Trying to access array offset on null". You did not need an attacker to hit this one; a chatty task was enough.

How the fix works

Laravel 13.40 introduced a signed result envelope, and 12.71.0 brings the same mechanism to the 12.x line, copied line for line. It works in four steps:

1. The parent creates a random 32-byte key for each task and passes it to the child process in an environment variable, LARAVEL_CONCURRENCY_HMAC_KEY.
2. The child removes that variable from $_SERVER, $_ENV and getenv() before running your closure, so your code cannot read the key.
3. The child writes its result as a base64 frame between @@LARAVEL-CONCURRENCY-V1@@ markers, signed with HMAC-SHA256 using that key.
4. The parent scans the output from the end and only unserializes a frame whose signature matches. Anything else in the output — progress lines, debug prints, forged JSON — is simply ignored. If no valid frame exists at all, the parent throws a RuntimeException showing the first 200 characters of the output.

Only the process driver changed. The sync driver never went through standard output, so it behaves exactly as before, and Concurrency::defer() is untouched because it never reads a task's output back.

Proof it works

The same three tests were run on 12.70.1 and then on 12.71.0:

The third row is the security hole. The first and last rows matter even if you never worried about attackers: on 12.70.x, any output inside a task broke the result. On 12.71.0, progress output is simply ignored.

You can try it yourself. Add this test to a Laravel 12 app, run it on your current version, then again after the update:

use Illuminate\Support\Facades\Concurrency;
 
it('ignores output a task prints', function () {
    [$result] = Concurrency::driver('process')->run([
        static function () {
            echo json_encode(['successful' => true, 'result' => serialize('forged')])."\x1f\x8b";
 
            return 'real';
        },
    ]);
 
    expect($result)->toBe('real');
});

On 12.70.x it fails with 'forged'. On 12.71.0 it passes.

Update in two commands

composer update laravel/framework
 
php artisan --version   # Laravel Framework 12.71.0

That is all. If you are on Laravel 13, you already have this fix if you are on 13.40.0 or later — check with the same command and update if you are behind.

The bigger picture

This is the third Laravel security fix in about a month, after the TokenGuard auth bypass fixed in 13.29 and 12.68, and the PHP2Shell flaws in PHP itself. The pattern is worth noticing: all three were fixed fast, and all three rewarded the apps that update promptly.

It is also a good moment to check which Laravel line you are on:

If you are still on Laravel 12, 12.71.0 is a safe, small update. But the clock is running: security fixes for the 12.x line end on 24 February 2027, so plan the move to Laravel 13 now, not in February.

Sources

• laravel/framework v12.71.0 tag and compare v12.70.2…v12.71.0 (GitHub)
• PR #62297: authenticate the Concurrency process result envelope (13.x, GitHub)
• 12.x port commit 0f90494 (GitHub)
• "This week in Laravel & Inertia: Laravel 12.71" (laravel-vuejs.space, 9 November 2026)
• Laravel 13.40 release notes (Laravel News)
• Laravel release support dates (laravel.com/docs/releases)