CVE-2019-6111

An issue was discovered in OpenSSH 7.9. Due to the scp implementation being derived from 1983 rcp, the server chooses which files/directories are sent to the client. However, the scp client only performs cursory validation of the object name returned (only directory traversal attacks are prevented). A malicious scp server (or Man-in-The-Middle attacker) can overwrite arbitrary files in the scp client target directory. If recursive operation (-r) is performed, the server can manipulate subdirectories as well (for example, to overwrite the .ssh/authorized_keys file).

Mitigation

This issue only affects the users of scp binary which is a part of openssh-clients package. Other usage of SSH protocol or other ssh clients is not affected. Administrators can uninstall openssh-clients for additional protection against accidental usage of this binary. Removal of openssh-clients package will make the packaged binaries like scp, ssh etc unavailable.

Note: This flaw requires a malicious MITM scp server for exploitation. Use cases where trusted SCP servers are used are not affected by this flaw.