The cert_TestHostName function in lib/certdb/certdb.c in the certificate-checking implementation in Mozilla Network Security Services (NSS) before 3.16 accepts a wildcard character that is embedded in an internationalized domain name's U-label, which might allow man-in-the-middle attackers to spoof SSL servers via a crafted certificate.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.