# CVE-2026-45133: Symfony Yaml uncontrolled recursion in parser

Source: https://junglewise.ai/threats/cve-2026-45133-symfony-yaml-uncontrolled-recursion-in-parser  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-14. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-45133 · Severity: medium · CVSS 4 · Published 2026-07-14

Symfony, a popular framework for building PHP web applications, contains a vulnerability in its YAML parsing component. An attacker can send a specially crafted document with deeply nested data structures to crash the web server. This results in a denial-of-service, making the application unavailable to legitimate users.

Technologies: [symfony/symfony (Packagist)](https://junglewise.ai/threats/technologies/symfony-symfony), [symfony/yaml (Packagist)](https://junglewise.ai/threats/technologies/symfony-yaml), [Symfony Yaml](https://junglewise.ai/threats/technologies/yaml). Vendors: [Packagist](https://junglewise.ai/threats/vendors/packagist), [Symfony](https://junglewise.ai/threats/vendors/symfony).

## Quick answers

**Is CVE-2026-45133 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-45133 being exploited in the wild.

**How severe is CVE-2026-45133?** Medium severity, with a CVSS score of 4, published 14 July 2026.

**Which products and versions are affected?** symfony/symfony (Packagist) ECOSYSTEM:introduced=0,fixed=5.4.52; symfony/yaml (Packagist) ECOSYSTEM:introduced=0,fixed=5.4.52; Symfony Yaml < 5.4.52, >= 6.0.0 < 6.4.40, >= 7.0.0 < 7.4.12, >= 8.0.0 < 8.0.12.

**Is there a fix for CVE-2026-45133?** Yes. symfony/symfony (Packagist): upgrade to 5.4.52 or later; symfony/yaml (Packagist): upgrade to 5.4.52 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-45133 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-45133?** Check whether you run symfony/symfony (Packagist), symfony/yaml (Packagist) or Symfony Yaml at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- symfony/symfony (Packagist): upgrade to 5.4.52 or later

  ```sh
  composer require symfony/symfony:^5.4.52
  ```

- symfony/yaml (Packagist): upgrade to 5.4.52 or later

  ```sh
  composer require symfony/yaml:^5.4.52
  ```


## Technical details

The vulnerability is classified as uncontrolled recursion (CWE-674) within Symfony's Yaml component. Specifically, both the block-level parser (Parser::parseBlock()) and inline parsers (Inline::parseSequence() and Inline::parseMapping()) fail to enforce a depth limit when processing nested structures. If an application exposes these parsers to attacker-controlled input, a remote, unauthenticated attacker can provide a crafted YAML document that triggers infinite or excessive recursion. This leads to PHP stack exhaustion and a crash of the worker process, resulting in a denial-of-service (DoS). The issue is resolved by bounding the recursion depth in the affected versions.

## Affected products

- Symfony Symfony < 5.4.52, >= 6.0.0-BETA1 < 6.4.40, >= 7.0.0-BETA1 < 7.4.12, >= 8.0.0-BETA1 < 8.0.12

## Identifiers

- CVE-2026-45133
- GHSA-c2p3-7m5p-cv8x

## Timeline

- 2026-05-20: patched: Security releases 5.4.52, 6.4.40, 7.4.12, and 8.0.12 published.
- 2026-07-14: disclosed: CVE-2026-45133 published.

## References

- [https://github.com/symfony/symfony/releases/tag/v5.4.52](https://github.com/symfony/symfony/releases/tag/v5.4.52)
- [https://github.com/symfony/symfony/releases/tag/v6.4.40](https://github.com/symfony/symfony/releases/tag/v6.4.40)
- [https://github.com/symfony/symfony/releases/tag/v7.4.12](https://github.com/symfony/symfony/releases/tag/v7.4.12)
- [https://github.com/symfony/symfony/releases/tag/v8.0.12](https://github.com/symfony/symfony/releases/tag/v8.0.12)
- [https://github.com/symfony/symfony/security/advisories/GHSA-c2p3-7m5p-cv8x](https://github.com/symfony/symfony/security/advisories/GHSA-c2p3-7m5p-cv8x)

## Related threats

- [Symfony Yaml component ReDoS in parser and inline](https://junglewise.ai/threats/cve-2026-123792-the-symfony-yaml-components-inline-and-parser-parse-some-yaml)
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- [Symfony HTTP Foundation ReDoS in HeaderUtils::split()](https://junglewise.ai/threats/cve-2026-108082-symfony-is-a-php-framework-for-web-and-console-applications-and)
- [Symfony Routing improper dot-segment encoding in UrlGenerator](https://junglewise.ai/threats/cve-2026-48784-symfony-routing-improper-dot-segment-encoding-in-urlgenerator)
- [Symfony HtmlSanitizer XSS via incomplete URL attribute sanitization](https://junglewise.ai/threats/cve-2026-48761-symfony-htmlsanitizer-xss-via-incomplete-url-attribute)