An issue was discovered in Symfony 4.2.0 to 4.2.11 and 4.3.0 to 4.3.7. The ability to enumerate users was possible due to different handling depending on whether the user existed when making unauthorized attempts to use the switch users functionality. This is related to symfony/security.

References

• https://nvd.nist.gov/vuln/detail/CVE-2019-18886
• https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/security-http/CVE-2019-18886.yaml
• https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2019-18886.yaml
• https://github.com/symfony/symfony/releases/tag/v4.3.8
• https://symfony.com/blog/cve-2019-18886-prevent-user-enumeration-using-switch-user-functionality
• https://symfony.com/blog/symfony-4-3-8-released
• https://symfony.com/cve-2019-18886