Inefficient regular expression complexity in Symfony - CVE-2026-45305
Published: May 21, 2026
Vulnerability identifier: #VU132059
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-45305
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to inefficient regular expression complexity in Symfony\Component\Yaml\Parser::cleanup() when parsing crafted YAML input. A remote attacker can supply a specially crafted oversized %YAML directive header, comment line, or document marker line to cause a denial of service.
Affected software
Symfony
Debian Linux
symfony (Debian package)
Debian Linux
symfony (Debian package)
How to mitigate CVE-2026-45305
Install security update from vendor's website.
Symfony - addressed in versions 5.4.52, 6.4.40, 7.4.12, 8.0.12
symfony (Debian package) - addressed in versions 5.4.53+dfsg-0+deb12u1, 6.4.41+dfsg-0+deb13u1
symfony (Debian package) - addressed in versions 5.4.53+dfsg-0+deb12u1, 6.4.41+dfsg-0+deb13u1