symfony/symfony security advisory

CVE-2026-45077: Unauthenticated PHP Object Deserialization in MonologBridge server:log Listener in symfony/symfony

CVE-2026-45077 is a high-severity PHP object injection vulnerability in the PHP package symfony/symfony (CVSS 8.6), published 14 July 2026. It is fixed in 5.4.52, 6.4.40, 7.4.12 and 8.0.12, one per release line; earlier versions on each line are affected. It can be exploited without an account.

high 8.6 published 2026-07-14 · updated 2026-07-15

Affected versions: >= 2.0.0, < 5.4.52
>= 6.0.0, < 6.4.40
>= 7.0.0, < 7.4.12
>= 8.0.0, < 8.0.12
Fixed in: 5.4.52, 6.4.40, 7.4.12, 8.0.12
Newest release: 8.1.10
Severity: High · CVSS 8.6
Type: PHP object injection
CWE-502, CWE-668
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your symfony/symfony version affected?

Run composer show symfony/symfony in your project, then enter the version. We check it against this and every other known symfony/symfony advisory.

Who can exploit CVE-2026-45077

Access: No account. Anyone who can send a request to an app that uses the affected code.

CVSS vector (scored by NVD): CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Your app is only exposed if it uses the affected part of symfony/symfony. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-45077 in symfony/symfony

Find the installed version: composer show symfony/symfony. If you never required it yourself, composer why symfony/symfony shows which package pulls it in.
Update it: composer update symfony/symfony --with-all-dependencies. You need the fixed version for your release line (5.4.52, 6.4.40, 7.4.12 and 8.0.12).
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "symfony/symfony": "^8.0.12" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-45077.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for PHP object injection issues while the upgrade waits. None of it replaces the fix.

Never pass user-controlled data to unserialize() or to template rendering, and restrict who can edit templates or settings.
Put a web application firewall in front of the app and watch for new PHP files or admin users.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-45077 advisory

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(base64_decode($message)) without authentication, integrity checks, or an allowed_classes 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.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-45077. Advisory title: “CVE-2026-45077: Unauthenticated PHP Object Deserialization in MonologBridge server:log Listener”.

References

GitHub security advisory GHSA-m7v2-7gxm-vc2v github.com
Symfony security advisory symfony.com
Fix commit 0891b2f github.com
Release v5.4.52 github.com
Release v6.4.40 github.com
Release v7.4.12 github.com
Release v8.0.12 github.com

Other symfony/symfony advisories

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Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.