It was discovered that Exim incorrectly handled memory in the ESMTP CHUNKING extension.
A remote attacker could use this issue to cause Exim to crash, resulting in a denial of service, or possibly execute arbitrary code. The default compiler options for affected releases should reduce the vulnerability to a denial of service.
Refer to Ubuntu advisory USN-3493-1 for affected packages and patching details, or update with your package manager.
Following are links for downloading patches to fix the vulnerabilities: