It was discovered that Exim, Debian's default mail transfer agent, is vulnerable to command injection attacks in its DKIM processing code, leading to arbitrary code execution. (CVE-2011-1407)
The default configuration supplied by Debian does not expose this vulnerability.
The oldstable distribution (lenny) is not affected by this problem.
For the stable distribution (squeeze), this problem has been fixed in version 4.72-6+squeeze2.
For the unstable distribution (sid), this problem has been fixed in version 4.76-1.
We recommend that you upgrade your exim4 packages.