Drupal 6.x before 6.16 and 5.x before version 5.22 does not properly block users under certain circumstances. A user with an open session that was blocked could maintain their session on the Drupal site despite being blocked.

References

• https://nvd.nist.gov/vuln/detail/CVE-2010-2473
• https://security-tracker.debian.org/tracker/CVE-2010-2473
• https://www.drupal.org/node/731710
• https://www.openwall.com/lists/oss-security/2010/06/28/8