Denial of Service Vulnerability in Symfony Yaml Component
CVE-2026-123792

8.7HIGH

Key Information:

Vendor

Sensiolabs

Status
Symfony
Vendor
CVE Published:
6 November 2026

What is CVE-2026-123792?

The Symfony Yaml components' Inline and Parser inefficiently parse specific YAML documents, leading to excessive processing times. A crafted YAML input can keep a PHP process occupied for extended durations, significantly impacting application performance. The parser repeatedly processes identical elements and patterns, causing processing time to increase exponentially with nested data structures. This vulnerability affects all code that parses untrusted YAML data, especially when default flags are used, allowing unauthenticated requests to exploit the issue effectively.

Affected Version(s)

symfony 0 < 5.4.56

symfony 6.0.0 < 6.4.50

symfony 7.0.0 < 7.4.23

References

https://github.com/symfony/symfony/security/advisories/GH...
third-party-advisory
https://github.com/symfony/symfony/commit/487f63bf2cacebc...
patch
https://github.com/symfony/symfony/commit/08db22d52e5d3e6...
patch

CVSS V4

Score:
8.7
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Sebastian Bergmann
Nicolas Grekas
.