GHSA-m7v2-7gxm-vc2v CVE-2026-45077
Symfony has Unauthenticated PHP Object Deserialization in MonologBridge server:log Listener
- Severity
- 0.0 / 10
- High · CVSS 4.0
- Exploit chance (EPSS)
- 0.67%
- Chance of exploitation in the next 30 days. Higher than 51.86% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
- Available
- 2 packages have a fixed version
Description
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
0.0.0.0:9911by default; it accepts connections on every interface, not only loopback. - Each received frame is processed as
unserialize(base64_decode($message))without anallowed_classesallowlist, without authentication, and without any integrity check. The decoded value is then passed todisplayLog(..., 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 versions
Packagist
| Package | Vulnerable | Fixed in |
|---|---|---|
| symfony/monolog-bridge | < 5.4.52 |
5.4.52 |
| symfony/monolog-bridge | >= 6.0.0, < 6.4.40 |
6.4.40 |
| symfony/monolog-bridge | >= 7.0.0, < 7.4.12 |
7.4.12 |
| symfony/monolog-bridge | >= 8.0.0, < 8.0.12 |
8.0.12 |
| symfony/symfony | < 5.4.52 |
5.4.52 |
| symfony/symfony | >= 6.0.0, < 6.4.40 |
6.4.40 |
| symfony/symfony | >= 7.0.0, < 7.4.12 |
7.4.12 |
| symfony/symfony | >= 8.0.0, < 8.0.12 |
8.0.12 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
symfony/monolog-bridge Packagist → 5.4.52
- composer
composer require symfony/monolog-bridge:^5.4.52
symfony/symfony Packagist → 5.4.52
- composer
composer require symfony/symfony:^5.4.52
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- High
- Integrity (vulnerable system)
- High
- Availability (vulnerable system)
- High
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
- Exploit maturity
- Unreported
CVSS 3.1 8.6
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- Low
- Availability
- High
Weakness
CWE-502: Deserialization of Untrusted Data
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
How to prevent it
- Architecture and Design, Implementation: If available, use the signing/sealing features of the programming language to assure that deserialized data has not been tainted. For example, a hash-based message authentication code (HMAC) could be used to ensure that data has not been modified.
- Implementation: When deserializing data, populate a new object rather than just deserializing. The result is that the data flows through safe input validation and that the functions are safe.
- Implementation: Explicitly define a final object() to prevent deserialization.
- Architecture and Design, Implementation: Make fields transient to protect them from deserialization. An attempt to serialize and then deserialize a class containing transient fields will result in NULLs where the transient data should be. This is an excellent way to prevent time, environment-based, or sensitive variables from being carried over and used improperly.
- Implementation: Avoid having unnecessary types or gadgets (a sequence of instances and method invocations that can self-execute during the deserialization process, often found in libraries) available that can be leveraged for malicious ends. This limits the potential for unintended or unauthorized types and gadgets to be leveraged by the attacker. Add only acceptable classes to an allowlist. Note: new gadgets are constantly being discovered, so this alone is not a sufficient mitigation.
- Architecture and Design, Implementation: Employ cryptography of the data or code for protection. However, it's important to note that it would still be client-side security. This is risky because if the client is compromised then the security implemented on the client (the cryptography) can be bypassed.
- Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
CWE-668: Exposure of Resource to Wrong Sphere
The product exposes a resource to the wrong control sphere, providing unintended actors with inappropriate access to the resource.
References
Packages
Other links
- github.com/symfony/symfony/security/advisories/GHSA-m7v2-7gxm-vc2v
- github.com/symfony/symfony/commit/0891b2f293896c488e26943dc034334364b77fc4
- github.com/FriendsOfPHP/security-advisories/blob/master/symfony/monolog-bridge/…
- github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-202…
- symfony.com/cve-2026-45077
- github.com/symfony/symfony/releases/tag/v5.4.52
- github.com/symfony/symfony/releases/tag/v6.4.40
- github.com/symfony/symfony/releases/tag/v7.4.12
- github.com/symfony/symfony/releases/tag/v8.0.12
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-2v3c-qxhr-7vpv Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process | High | Also affects symfony/symfony |
| GHSA-r925-mgvr-h9cc Symfony: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header | High | Also affects symfony/symfony |
| GHSA-h5x3-xfc9-m39h Symfony: UrlGenerator Dot-Segment Encoding Skips Every Other Chained `../` or `./` → Generated URL Collapses Off-Route Under RFC 3986 Normalization | Medium | Also affects symfony/symfony |
| GHSA-v3wm-qf9p-c549 Symfony: HtmlSanitizer URL Parser Deny Gates Underinclusive: Percent-Encoded BiDi Marks and Unicode Whitespace Bypass Visual-Spoofing Defense | Medium | Also affects symfony/symfony |
| GHSA-rrj9-5q2j-4gvr Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade | Medium | Also affects symfony/symfony |
| GHSA-38cx-cq6f-5755 Symfony: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient | High | Also affects symfony/symfony |
| GHSA-6h46-9jf5-q59x Symfony: Security Firewall Bypass via failure_forward Subrequest: Unauthenticated Access to access_control-Protected GET Routes | High | Also affects symfony/symfony |
| GHSA-x5qj-865h-mgvm Symfony: HtmlSanitizer UrlAttributeSanitizer Misses URL Attributes | Medium | Also affects symfony/symfony |
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