What’s Vulnerable › Vulnerabilities

CVE-2016-4423

• Severity: high (CVSS 7.5 v3.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2016-06-01 · updated 2026-06-17
• Weakness: CWE-399

Description

The attemptAuthentication function in Component/Security/Http/Firewall/UsernamePasswordFormAuthenticationListener.php in Symfony before 2.3.41, 2.7.x before 2.7.13, 2.8.x before 2.8.6, and 3.0.x before 3.0.6 does not limit the length of a username stored in a session, which allows remote attackers to cause a denial of service (session storage consumption) via a series of authentication attempts with long, non-existent usernames.

Affected products

• Debian Linux: 8.0
• symfony: through 2.3.40; 2.7.0, 2.7.1, 2.7.2, 2.7.3, 2.7.4, 2.7.5 (+19)

References

• http://www.debian.org/security/2016/dsa-3588
• https://github.com/symfony/symfony/pull/18733
• https://symfony.com/blog/cve-2016-4423-large-username-storage-in-session
• http://www.debian.org/security/2016/dsa-3588
• https://github.com/symfony/symfony/pull/18733
• https://symfony.com/blog/cve-2016-4423-large-username-storage-in-session

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