SymfonyFramework / library · Sensiolabs
CVE-2026-45305
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, Symfony\Component\Yaml\Parser::cleanup() used regular expressions with overlapping quantifiers for YAML directive, comment, and document marker cleanup, allowing crafted input to make parsing hang for an arbitrarily long time. 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's cleanup() method uses regular expressions with overlapping quantifiers for processing YAML directives, comments, and document markers. Crafted YAML input with specific patterns can trigger catastrophic backtracking, causing the parser to hang indefinitely (ReDoS vulnerability).
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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Determine installed Symfony versionRun `bin/console --version` or check the `symfony/symfony` or `symfony/framework-bundle` version in your `composer.lock` or `composer.json` fileAffected if The version is less than 5.4.52, or 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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Identify if YAML component is in useCheck your `composer.lock` for the presence of `symfony/yaml` package and note its versionAffected if The symfony/yaml package version matches the vulnerable version ranges listed above
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Check for YAML input from external sourcesSearch your codebase for usages of `Yaml::parse()` or the YamlParser service that process input from user requests, API endpoints, or file uploadsAffected if Your application parses YAML input from untrusted or external sources without prior sanitization
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Review YAML parsing configurationExamine your application configuration and code that configures or invokes the YAML parser, particularly any custom regex patterns in YAML processingAffected if Custom YAML processing is enabled and the cleanup() method in the YAML parser handles complex or nested YAML documents
You are affected if your Symfony version falls within the vulnerable ranges AND your application parses YAML input from untrusted sources using the vulnerable cleanup() method.
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 to version 5.4.52, 6.4.40, 7.4.12, 8.0.12 or later to replace the vulnerable regex patterns. If upgrade is not immediately possible, sanitize or limit YAML input from untrusted sources.
Upgrade to Symfony 5.4.52, 6.4.40, 7.4.12, or 8.0.12 depending on your current major version branch
- Identify your current Symfony version by checking composer.json or running `composer show symfony/symfony | grep version`
- Update your composer.json to require the appropriate fixed version based on your current branch: for 5.x use ^5.4.52, for 6.x use ^6.4.40, for 7.x use ^7.4.12, or for 8.x use ^8.0.12
- Run `composer update symfony/symfony --with-all-dependencies` to install the patched version
- Verify the correct version is installed by running `composer show symfony/symfony | grep version`
- Run your application's test suite to confirm the upgrade does not break existing functionality
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Symfony
Scoped from the published advisory
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 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 $1,376.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-45305 — 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-2026-45305 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
- No weaponised exploit code, or anything meant to cause harm
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