Exim is prone to an arbitrary code-execution vulnerability. An attacker can exploit this issue to execute arbitrary code with root privileges. Exim versions 4.8 through 4.92.1 are vulnerable.
Permit local access for trusted individuals only. Where possible, use restricted environments and restricted shells.
Permit access to systems for trusted and accountable individuals only.
Block external access at the network boundary, unless external parties require service.
If global access isn’t needed, filter access to the affected device at the network boundary. Restricting access to only trusted computers and networks might greatly reduce the likelihood of exploitation.
Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to monitor network traffic for signs of anomalous or suspicious activity. This includes but is not limited to requests that include explained incoming and outgoing traffic. This may indicate exploit attempts to activity that results from successful exploits.
Implement multiple redundant layers of security.
Since this issue may be leveraged to execute code, we recommend memory-protection schemes, such as nonexecutable stack/heap configurations and randomly mapped memory segments. This tactic may complicate exploits of memory-corruption vulnerabilities.
Updates are available. Please see the references or vendor advisory for more information.
www.exim.org/
bugzilla.redhat.com/show_bug.cgi?id=1748397
git.exim.org/exim.git/commitdiff/2600301ba6dbac5c9d640c87007a07ee6dcea1f4
github.com/Exim/exim/tree/exim-4.92.2%2Bfixes/doc/doc-txt/cve-2019-15846
www.tenable.com/blog/cve-2019-15846-unauthenticated-remote-command-execution-flaw-disclosed-for-exim