How severe is CVE-2026-45077?

No CVSS score has been assigned to CVE-2026-45077 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-45077?

CVE-2026-45077 affects the following packages: symfony/monolog-bridge (Packagist), symfony/symfony (Packagist), symfony/monolog-bridge (Packagist), symfony/monolog-bridge (Packagist), symfony/monolog-bridge (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-45077?

Update symfony/monolog-bridge to 5.4.52 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45077 is resolved across your whole dependency graph.

How do I detect CVE-2026-45077 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/monolog-bridge, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-45077 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Is CVE-2026-45077 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-45077 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-45077?

CVE-2026-45077 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 50th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-45077?

CVE-2026-45077 is classified as Deserialization of Untrusted Data (CWE-502), CWE-668 (CWE-668). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-45077 published, and has it been updated?

CVE-2026-45077 was published on July 14, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘 Packagist

Not in CISA KEV

CVE-2026-45077 — monolog-bridge

Fix: symfony/symfony@0891b2f

CVE-2026-45077 is a Deserialization of Untrusted Data vulnerability in symfony/monolog-bridge. A fix is available for symfony/monolog-bridge — see the affected versions and patch details below.

Symfony: Unauthenticated PHP Object Deserialization in MonologBridge server:log Listener

Also known asGHSA-m7v2-7gxm-vc2v

Published

Jul 14, 2026

Updated

Aug 12, 2026

Affected

8 pkgs

Patched

8 / 8

Exploits

None indexed

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-45077.

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs50th percentile — riskier than 50% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

8 pkgs affected

🐘symfony/monolog-bridge🐘symfony/symfony🐘symfony/monolog-bridge🐘symfony/monolog-bridge🐘symfony/monolog-bridge🐘symfony/symfony🐘symfony/symfony🐘symfony/symfony

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

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:

The listener binds to 0.0.0.0:9911 by default; it accepts connections on every interface, not only loopback.
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.

Affected Packages

8 total 8 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`symfony/monolog-bridge`	all versions	5.4.52`composer require symfony/monolog-bridge:^5.4.52`
🐘Packagist	`symfony/symfony`	all versions	5.4.52`composer require symfony/symfony:^5.4.52`
🐘Packagist	`symfony/monolog-bridge`	≥ 6.0.0&&< 6.4.40	6.4.40`composer require symfony/monolog-bridge:^6.4.40`
🐘Packagist	`symfony/monolog-bridge`	≥ 7.0.0&&< 7.4.12	7.4.12`composer require symfony/monolog-bridge:^7.4.12`
🐘Packagist	`symfony/monolog-bridge`	≥ 8.0.0&&< 8.0.12	8.0.12`composer require symfony/monolog-bridge:^8.0.12`
🐘Packagist	`symfony/symfony`	≥ 6.0.0&&< 6.4.40	6.4.40`composer require symfony/symfony:^6.4.40`

Affected Products

1 product · 4 configurations

Application

symfonysensiolabs

≥ 8.0.0 && < 8.0.12

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/monolog-bridge, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update symfony/monolog-bridge to 5.4.52 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45077 is resolved across your whole dependency graph.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Frequently Asked Questions

### 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 integr