Package Instance

Improper Authentication
An issue was discovered in the Ldap component in Symfony. It allows remote attackers to bypass authentication by logging in with a `null` password and valid username, which triggers an unauthenticated bind.

Prevent user enumeration using Guard or the new Authenticator-based Security
Description
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The ability to enumerate users was possible without relevant permissions due to different exception messages depending on whether the user existed or not. It was also possible to enumerate users by using a timing attack, by comparing time elapsed when authenticating an existing user and authenticating a non-existing user.

Resolution
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We now ensure that 403s are returned whether the user exists or not if the password is invalid or if the user does not exist.

The patch for this issue is available [here](https://github.com/symfony/symfony/commit/2a581d22cc621b33d5464ed65c4bc2057f72f011) for branch 3.4.

Credits
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I would like to thank James Isaac and Mathias Brodala for reporting the issue and Robin Chalas for fixing the issue.

Empty passwords validation issue
Validating a user password with a `UserPassword` constraint but with no `NotBlank` constraint passes without any error (the empty password would not be compared with the user password). Note that you should always be explicit and add a `NotBlank` constraint, but as it worked before without, it's considered as a backward compatibility break and a security issue.