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SymfonyFramework / library · Sensiolabs

CVE-2026-45753

MEDIUM · 6.1 CVSS v3.1 Published 2026-07-14
Fix available
A fix is available. Upgrade to 6.4.40 / 7.4.12 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges 5 weeks old

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 · unedited
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. From 6.1.0-BETA1 until 6.4.40, 7.4.12, and 8.0.12, UrlAttributeSanitizer::getSupportedAttributes() omits URL-valued attributes including action, formaction, poster, and cite, so configurations that admit those attributes can leave javascript: URIs unsanitized and enable XSS when the resulting HTML is rendered or a victim submits a form or clicks a button. This issue is fixed in versions 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 confidence

The Symfony UrlAttributeSanitizer::getSupportedAttributes() method omits URL-valued attributes (action, formaction, poster, cite) from sanitization, allowing javascript: URIs to pass through unsanitized. This enables XSS when the affected HTML is rendered or users interact with forms/buttons using these attributes.

MitigationUpgrade Symfony to version 6.4.40, 7.4.12, or 8.0.12 to patch the missing attribute sanitization, or explicitly filter javascript: URIs in any custom sanitizer configurations.

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
Affected:>= 6.1.0, < 6.4.40>= 7.0.0, < 7.4.12>= 8.0.0, < 8.0.12

CVSS 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
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Symfony version
    Run `composer show symfony/framework-bundle` or check your composer.lock file for the symfony/* packages version
    Affected if The version falls within 6.1.0 to <6.4.40, 7.0.0 to <7.4.12, or 8.0.0 to <8.0.12
  2. Locate HtmlSanitizer configuration
    Search for files containing `HtmlSanitizer` or `url_sanitizer` in your config directory (config/packages/ or similar)
    Affected if A sanitizer is configured that handles HTML with URL-valued attributes
  3. Check for usage of vulnerable attributes
    Search templates and user-input handling code for `action=`, `formaction=`, `poster=`, or `cite=` attributes in HTML elements
    Affected if Your application renders HTML containing these attributes from user-supplied or unsanitized sources
  4. Verify if sanitizer processes these attributes
    Inspect your HtmlSanitizer configuration for an `allowed_link_attributes` or similar list, and confirm whether action, formaction, poster, cite are explicitly allowed or missing from sanitization
    Affected if The sanitizer configuration does not explicitly strip or sanitize javascript: URIs from these attributes
  5. Test for javascript: URI injection
    Submit or render a test input containing `<form action="javascript:alert(1)">`, `<button formaction="javascript:alert(1)">`, `<video poster="javascript:alert(1)">`, or `<blockquote cite="javascript:alert(1)">` and inspect the output
    Affected if The javascript: scheme passes through unchanged in the rendered HTML

Your environment is affected if you run a vulnerable Symfony version (6.1.0-6.4.39, 7.0.0-7.4.11, or 8.0.0-8.0.11) and use the HtmlSanitizer to process HTML containing action, formaction, poster, or cite attributes from untrusted sources.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 6.4.40 / 7.4.12 / 8.0.12 or later
Fixed in 6.4.407.4.128.0.12
Interim mitigation

Upgrade Symfony to version 6.4.40, 7.4.12, or 8.0.12 to patch the missing attribute sanitization, or explicitly filter javascript: URIs in any custom sanitizer configurations.

Recommended fix High confidence

6.4.40, 7.4.12, or 8.0.12 depending on current major version

  1. Determine current Symfony version by checking composer.json or running composer show symfony/http-kernel (or similar Symfony component)
  2. If using Symfony 6.x (>=6.1.0, <6.4.40), upgrade to version 6.4.40: composer require symfony/http-kernel:^6.4.40 symfony/framework-bundle:^6.4.40 (and other Symfony components to ^6.4.40)
  3. If using Symfony 7.x (>=7.0.0, <7.4.12), upgrade to version 7.4.12: composer require symfony/http-kernel:^7.4.12 symfony/framework-bundle:^7.4.12 (and other Symfony components to ^7.4.12)
  4. If using Symfony 8.x (>=8.0.0, <8.0.12), upgrade to version 8.0.12: composer require symfony/http-kernel:^8.0.12 symfony/framework-bundle:^8.0.12 (and other Symfony components to ^8.0.12)
  5. Run composer update to apply changes
  6. Clear Symfony cache: php bin/console cache:clear
  7. Run test suite to verify application functions correctly after upgrade
Caveat Minor version upgrades in Symfony typically have minimal breaking changes; however, review Symfony's changelog for the specific version upgrade for any potential impacts

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Symfony Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,900
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-45753 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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  • No spam, self-promotion, credentials, or personal data