SymfonyFramework / library · Sensiolabs
CVE-2026-45304
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 resolved YAML collection aliases recursively, allowing a small untrusted YAML input to expand into a multi-gigabyte structure and exhaust memory. 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 confidenceThe Symfony YAML Parser resolves YAML collection aliases (anchors/aliases) recursively, allowing a small malicious YAML input to expand exponentially into multi-gigabyte data structures. This causes memory exhaustion and denial of service - a classic 'billion laughs' attack adapted for YAML.
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 if Symfony YAML component is in useSearch your codebase for 'Symfony\Component\Yaml' usage, check composer.json for symfony/yaml in requires, or look for the vendor/symfony/yaml directoryAffected if The symfony/yaml package is present in the project dependencies
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Determine installed Symfony YAML versionRun 'composer show symfony/yaml' or check the version listed in composer.lock under the symfony/yaml packageAffected if The installed version is below 5.4.52, or between 6.0.0 and 6.4.39, or between 7.0.0 and 7.4.11, or between 8.0.0 and 8.0.11
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Check if application parses untrusted YAML inputSearch code for Yaml::parse() or Parser calls where input来源 includes user data: HTTP request parameters, uploaded files, API payloads, or external configuration filesAffected if The application parses YAML input that originates from users or external sources without sanitization
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Verify YAML parser alias expansion behaviorTest the parser with a known YAML alias expansion payload (e.g., &a [*a,*a,*a,*a]) to observe if the parser expands recursively without limitsAffected if The parser expands anchors recursively, allowing exponential growth from small input
You are affected if Symfony YAML component is used to parse untrusted YAML input and the installed version falls within any of the vulnerable ranges listed.
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 versions 5.4.52, 6.4.40, 7.4.12, or 8.0.12. If upgrading is not immediately feasible, sanitize or reject untrusted YAML input before parsing.
Upgrade to 5.4.52, 6.4.40, 7.4.12, or 8.0.12 depending on your current major version branch
- Identify the current Symfony version by checking composer.json or the installed version
- Determine which major version branch you are on (5.x, 6.x, 7.x, or 8.x)
- Run 'composer require symfony/symfony:^5.4.52' for 5.x branches, 'composer require symfony/symfony:^6.4.40' for 6.x branches, 'composer require symfony/symfony:^7.4.12' for 7.x branches, or 'composer require symfony/symfony:^8.0.12' for 8.x branches
- Run 'composer update symfony/symfony' to apply the upgrade
- Verify the installed version matches the target patch version using 'composer show symfony/symfony'
- Run your test suite to ensure the upgrade does not break existing functionality
- Deploy the updated application
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Symfony
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-45304 — 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-2026-45304 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
- No spam, self-promotion, credentials, or personal data