The XML Security Library is a C library based on libxml2 and OpenSSL. Itimplements the XML Signature Syntax and Processing and XML EncryptionSyntax and Processing standards. HMAC is used for message authenticationusing cryptographic hash functions. The HMAC algorithm allows the hashoutput to be truncated (as documented in RFC 2104).A missing check for the recommended minimum length of the truncated form ofHMAC-based XML signatures was found in xmlsec1. An attacker could use thisflaw to create a specially-crafted XML file that forges an XML signature,allowing the attacker to bypass authentication that is based on the XMLSignature specification. (CVE-2009-0217)Users of xmlsec1 should upgrade to these updated packages, which containa backported patch to correct this issue. After installing the updatedpackages, applications that use the XML Security Library must be restartedfor the update to take effect.