Unspecified vulnerability in session.c in PHP before 5.1.3 has unknown impact and attack vectors, related to "certain characters in session names," including special characters that are frequently associated with CRLF injection, SQL injection, cross-site scripting (XSS), and HTTP response splitting vulnerabilities.  NOTE: while the nature of the vulnerability is unspecified, it is likely that this is related to a violation of an expectation by PHP applications that the session name is alphanumeric, as implied in the PHP manual for session_name().