CVE-2026-45077: Symfony: Unauthenticated PHP Object Deserialization in MonologBridge server:log Listener
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(base64decode($message)) without an allowedclasses allowlist, without authentication, and without any integrity check. The decoded value is then passed to displayLog(..., array $record) which assumes (without validating) that the result is an array.
Any host that can reach TCP port 9911 on a machine running server:log can therefore submit attacker-chosen serialized PHP payloads. The minimum impact is an unauthenticated denial of service (sending a non-array, e.g. serialize(new stdClass()), crashes the listener with a type error). Object injection with magic-method side effects (wakeup() / destruct() / etc.) is reachable before the array type-check fires; full remote code execution is environment-dependent and contingent on usable gadget chains in the autoload set of the target process.
Resolution
The server:log command no longer binds to all interfaces by default: the default --host is now 127.0.0.1:9911, requiring explicit opt-in to accept off-host traffic. Message decoding is gated by an unserialize() allowlist restricted to the Symfony\Component\VarDumper\Caster\ and Symfony\Component\VarDumper\Cloner\ classes that legitimately appear inside dumped log records; any other class is rejected and the record discarded.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Toàn Thắng and Sam Sanoop for reporting the issue and Nicolas Grekas for fixing it.
Other sources
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12, the server:log listener (Symfony\Bridge\Monolog\Command\ServerLogCommand) binds to 0.0.0.0:9911 by default and processes each received frame with unserialize(base64decode($message)) without authentication, integrity checks, or an allowedclasses allowlist, allowing any reachable host to submit attacker-chosen serialized PHP payloads that can crash the listener and may trigger object-injection gadget effects. This issue is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 8.0.12 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 7.4.12 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 6.4.40 - Upgrade
Upgrade
composer/symfony/monolog-bridgeto a version that resolves this vulnerability.Fixed in 8.0.12 - Upgrade
Upgrade
composer/symfony/monolog-bridgeto a version that resolves this vulnerability.Fixed in 7.4.12 - Upgrade
Upgrade
composer/symfony/monolog-bridgeto a version that resolves this vulnerability.Fixed in 6.4.40 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 5.4.52 - Upgrade
Upgrade
composer/symfony/monolog-bridgeto a version that resolves this vulnerability.Fixed in 5.4.52 - Upgrade
Upgrade
Symfony (Symfony/Bridge/Monolog server:log listener)to a version that resolves this vulnerability.Fixed in 5.4.52 - Upgrade
Upgrade
Symfony (Symfony/Bridge/Monolog server:log listener)to a version that resolves this vulnerability.Fixed in 6.4.40 - Upgrade
Upgrade
Symfony (Symfony/Bridge/Monolog server:log listener)to a version that resolves this vulnerability.Fixed in 7.4.12 - Upgrade
Upgrade
Symfony (Symfony/Bridge/Monolog server:log listener)to a version that resolves this vulnerability.Fixed in 8.0.12 - Configuration
Ensure the server:log listener does not bind to all interfaces; use the default --host of 127.0.0.1:9911 (instead of 0.0.0.0:9911) or explicitly set --host to 127.0.0.1:9911 unless off-host traffic is required.
Symfony iations iamonolog bridge ServerLogCommand (server:log) --host default bind address = 127.0.0.1:9911 - Compensating control
If you cannot upgrade immediately, restrict network access to the TCP port used by server:log so that only local/authorized hosts can reach the listener (the issue states any host that can reach TCP port 9911 can submit payloads).
Event History
Frequently Asked Questions
What is the severity of CVE-2026-45077?
CVE-2026-45077 has a risk score of 76, indicating it is a high-severity vulnerability.
How do I fix CVE-2026-45077?
To mitigate CVE-2026-45077, update to a patched version of Symfony or configure your application to disable the server:log command if it is not needed in production.
What software is affected by CVE-2026-45077?
CVE-2026-45077 affects the Symfony framework and specifically the Symfony Monolog Bridge component.
What are the potential impacts of CVE-2026-45077?
Exploitation of CVE-2026-45077 could allow an attacker to gain unauthorized access to application log data and potentially execute remote code.
When was CVE-2026-45077 published?
CVE-2026-45077 was published on May 27, 2026.