GHSA-m7v2-7gxm-vc2v Symfony has Unauthenticated PHP Object Deserialization in MonologBridge server:log Listener

• Packagist symfony/monolog-bridge: < 5.4.52 → fixed in 5.4.52 • Packagist symfony/symfony: < 5.4.52 → fixed in 5.4.52 • Packagist symfony/monolog-bridge: >= 6.0.0, < 6.4.40 → fixed in 6.4.40 • Packagist symfony/monolog-bridge: >= 7.0.0, < 7.4.12 → fixed in 7.4.12 • Packagist symfony/monolog-bridge: >= 8.0.0, < 8.0.12 → fixed in 8.0.12 • Packagist symfony/symfony: >= 6.0.0, < 6.4.40 → fixed in 6.4.40 • Packagist symfony/symfony: >= 7.0.0, < 7.4.12 → fixed in 7.4.12 • Packagist symfony/symfony: >= 8.0.0, < 8.0.12 → fixed in 8.0.12

Description `Symfony\Bridge\Monolog\Command\ServerLogCommand` (the `server:log` console command) is a development-time helper that opens a TCP listener and displays log records pushed to it by the application's logging pipeline. Two unsafe defaults combine into a remotely reachable PHP object-deserialization sink: 1. The listener binds to `0.0.0.0:9911` by default; it accepts connections on every interface, not only loopback. 2. Each received frame is processed as `unserialize(base64_decode($message))` without an `allowed_classes` allowlist, without authentication, and without any integrity check. The decoded value is then passed to `displayLog(..., array $record)` which assumes (without validating) that the result is an array. Any host that can reach TCP port 9911 on a machine running `server:log` can therefore submit attacker-chosen serialized PHP payloads. The minimum impact is an unauthenticated denial of service (sending a non-array, e.g. `serialize(new stdClass())`, crashes the listener with a type error). Object injection with magic-method side effects (`__wakeup()` / `__destruct()` / etc.) is reachable before the array type-check fires; full remote code execution is environment-dependent and contingent on usable gadget chains in the autoload set of the target process. Resolution The `server:log` command no longer binds to all interfaces by default: the default `--host` is now `127.0.0.1:9911`, requiring explicit opt-in to accept off-host traffic. Message decoding is gated by an `unserialize()` allowlist restricted to the `Symfony\Component\VarDumper\Caster\*` and `Symfony\Component\VarDumper\Cloner\*` classes that legitimately appear inside dumped log records; any other class is rejected and the record discarded. The patch for this issue is available here for branch 5.4. Credits Symfony would like to thank Toàn Thắng and Sam Sanoop for reporting the issue and Nicolas Grekas for fixing it.