The remote host is missing an update to flex announced via advisory DSA 1020-1. Chris Moore discovered that flex, a scanner generator, generates code, which allocates insufficient memory, if the grammar contains REJECT statements or trailing context rules. This may lead to a buffer overflow and the execution of arbitrary code. If you use code, which is derived from a vulnerable lex grammar in an untrusted environment you need to regenerate your scanner with the fixed version of flex. The old stable distribution (woody) is not affected by this problem.
For the stable distribution (sarge) this problem has been fixed in version 2.5.31-31sarge1. For the unstable distribution (sid) this problem has been fixed in version 2.5.33-1. We recommend that you upgrade your flex package. https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201020-1