Discovered by: Chinmay Pandya
Email address: firstname.lastname@example.org
Issue discovered - 9 Jun 2020
CVE obtained - 16 Jul 2020
Vendor notified - 9 Jun 2020
Vendor acknowledgement received - 9 Jun 2020
Public disclosure 18 Jul 2020
scp is a program for copying files between computers. It uses the SSH protocol. It is included by default in most Linux and Unix distributions.
While coping files to remote server, file path is appended at end of local scp command. For example, if you execute following command
scp SourceFile user@host:directory/TargetFile
it will execute a local command
scp -t directory/TargetFile
At time of creating local scp command, it does not sanitize file name. An attacker can pass a backtick enabled payload as file name and when local scp command is executed, local shell will also execute backtick enabled payload.
Execute following command with scp
scp /sourcefile remoteserver:'`touch /tmp/exploit.sh`/targetfile'
After executing this command, go to remote server and you will see in /tmp/ directory that file exploit.sh is present. Putting single quotes in file name is important to prevent payload execution on local shell or using escape character like single quotes in file name can prevent payload execution on local shell
The scp command is a historical protocol (called rcp) which relies upon that style of argument passing and encounters expansion problems. It has proven very difficult to add “security” to the scp model. All attempts to “detect” and “prevent” anomalous argument transfers stand a great chance of breaking existing workflows. Yes, we recognize it the situation sucks. But we don’t want to break the easy patterns people use scp for, until there is a commonplace replacement. People should use rsync or something else instead if they are concerned.