Scp

wikipedia:Secure copy (scp) is a means of securely transferring computer files between a local host and a remote host or between two remote hosts. scp implements a progress bar to estimate transfers.

http://man7.org/linux/man-pages/man1/scp.1.html

scp help
usage: scp [-346ABCpqrTv] [-c cipher] [-F ssh_config] [-i identity_file]
            [-J destination] [-l limit] [-o ssh_option] [-P port]
            [-S program] source ... target

Example

scp your_username@your_server:/tmp/FILE ./
USERNAME@SERVER's password:
Could not chdir to home directory /home/USERNAME: No such file or directory
protocol error: mtime.sec not present

scp USERNAME@SERVER:/tmp/your_folder ./
scp: /tmp/your_folder: not a regular file

scp -r USERNAME@SERVER:/tmp/your_folder ./
scp: /tmp/your_folder/your_file: Permission denied

Security

According to OpenSSH developers in April 2019 the scp protocol is outdated, inflexible and not readily fixed; they recommend the use of more modern protocols like sftp and rsync for file transfer.

OpenSSH 8.3 May 2020 scp(1): when receiving files, scp(1) could be become desynchronised if a utimes (2) system call failed. This could allow file contents to be interpreted as file metadata and thereby permit an adversary to craft a file system that, when copied with scp(1) in a configuration that caused utimes(2) to fail (e.g. under a SELinux policy or syscall sandbox), transferred different file names and contents to the actual file system layout. Exploitation of this is not likely as utimes(2) does not fail under normal circumstances. Successful exploitation is not silent - the output of scp(1) would show transfer errors followed by the actual file(s) that were received. Finally, filenames returned from the peer are (since openssh-8.0) matched against the user's requested destination, thereby disallowing a successful exploit from writing files outside the user's selected target glob (or directory, in the case of a recursive transfer). This ensures that this attack can achieve no more than a hostile peer is already able to achieve within the scp protocol.

Activities

• Understand the differences between cp, scp and rsync: https://stackoverflow.com/questions/20244585/how-does-scp-differ-from-rsync
• Review security advisories related to scp: CVE-2019-6111 related to scp tool and protocol allowing to overwrite arbitrary files in the scp client target directory
• pv </dev/zero | ssh REMOTE_SERVER 'cat >/dev/null'

News

• OpenSSH 9.0 Aug 2022 https://www.openssh.com/txt/release-9.0 switches scp from using the legacy scp/rcp protocol to using the SFTP protocol by default

Related terms

• pscp (PuTTY)
• sftp
• jailkit
• magic-wormhole
• progress
• scp -3
• Resume transmissions: rsync -P or --partial --progress

See also

• sftp, sftp chroot configuration, Filezilla, Core FTP, sshfs, internal-sftp, sshd_config, SFTP protocol, Secure file transfer program (sftp)
• cp, dd, sftp, scp, rsync, casync, mv, fio, ln, docker cp, kubectl cp, minikube cp, multipass transfer, Copy-Item, Xcopy
• OpenSSH (changelog): /etc/ssh/sshd_config | /etc/ssh/ssh_config | ~/.ssh/ | openSSL | sshd logs | sftp | scp | authorized_keys | ssh-keygen | ssh-keyscan | ssh-add | ssh-agent | ssh | Ssh -O stop | ssh-copy-id | CheckHostIP | UseKeychain, OpenSSF

"OpenSSH 8.0". OpenSSH Release Notes. 17 April 2019.

https://nvd.nist.gov/vuln/detail/CVE-2019-6111