The sync endpoint in YubiKey Validation Server before 2.40 allows remote attackers to replay an OTP. NOTE: this issue is potentially relevant to persons outside Yubico who operate a self-hosted OTP validation service with a non-default configuration such as an open sync pool; the issue does NOT affect YubiCloud.

The verify endpoint in YubiKey Validation Server before 2.40 does not check the length of SQL queries, which allows remote attackers to cause a denial of service, aka SQL injection. NOTE: this issue is potentially relevant to persons outside Yubico who operate a self-hosted OTP validation service; the issue does NOT affect YubiCloud.