SymfonyFramework / library · Sensiolabs
CVE-2026-45133
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedSymfony 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, when the parser is exposed to attacker-controlled input, deeply nested mappings or sequences cause both the block-level (Parser::parseBlock()) and inline (Inline::parseSequence() / Inline::parseMapping()) parsers to recurse without a depth limit. A crafted document exhausts the PHP stack and crashes the worker. This issue is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceSymfony YAML parser lacks depth limiting on recursive parsing functions (Parser::parseBlock(), Inline::parseSequence(), Inline::parseMapping()). When processing attacker-controlled YAML input with deeply nested mappings or sequences, the parser recurses indefinitely until PHP stack exhaustion causes worker crash (DoS).
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
SymfonyFramework / library
< 5.4.52>= 6.0.0, < 6.4.40>= 7.0.0, < 7.4.12>= 8.0.0, < 8.0.12CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed Symfony versionRun `composer show sensiolabs/symfony` or inspect the version in vendor/sensiolabs/symfony/composer.json. Alternatively, run `php bin/console --version` to see the framework version.Affected if The installed version is below 5.4.52, between 6.0.0 and 6.4.39, between 7.0.0 and 7.4.11, or between 8.0.0 and 8.0.11.
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Confirm YAML component is in useSearch your codebase for YAML parsing calls such as Yaml::parse(), Parser::parse(), or direct instantiation of the Parser class. Check controller files, services, and configuration loaders for these patterns.Affected if Your application parses YAML input using the Symfony YAML component.
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Determine if parsed YAML originates from untrusted sourcesAudit the data flow feeding into YAML parsing functions. Identify whether input comes from user HTTP requests, uploaded files, external APIs, or other potentially attacker-controlled sources.Affected if Your application parses YAML from untrusted or user-supplied input without depth validation beforehand.
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Inspect recursive parsing functionsIf you have access to the vendor/sensiolabs/symfony directory, verify that Parser.php contains depth limiting logic in the parseBlock(), Inline::parseSequence(), and Inline::parseMapping() methods.Affected if The YAML component lacks depth limiting checks in these recursive parsing functions.
Your environment is affected if you run a Symfony version within the affected ranges AND your application parses untrusted or deeply nested YAML input using the Symfony YAML component.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped5.4.526.4.407.4.12
Upgrade Symfony framework to version 5.4.52, 6.4.40, 7.4.12, or 8.0.12 or later. If upgrade is not immediately feasible, restrict or validate YAML input depth before parsing.
5.4.52, 6.4.40, 7.4.12, or 8.0.12 (depending on your current major version branch)
- 1. Identify your current Symfony version by checking your composer.json or running `composer show symfony/symfony | grep version`
- 2. Determine which version branch you're on (5.x, 6.x, 7.x, or 8.x)
- 3. Run `composer require symfony/symfony:^5.4.52` if on 5.4.x, `composer require symfony/symfony:^6.4.40` if on 6.x, `composer require symfony/symfony:^7.4.12` if on 7.x, or `composer require symfony/symfony:^8.0.12` if on 8.x
- 4. Run `composer update symfony/symfony` to apply the upgrade
- 5. Run your test suite to verify the upgrade does not break functionality
- 6. Deploy the updated version to production
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Symfony
Scoped from the published advisory
- Consultation1.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,144.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-45133 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-45133 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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