In OpenSSH 7.9, due to accepting and displaying arbitrary stderr output from the server, a malicious server (or Man-in-The-Middle attacker) can manipulate the client output, for example to use ANSI control codes to hide additional files being transferred.
https://sintonen.fi/advisories/scp-client-multiple-vulnerabilities.txt
https://security.netapp.com/advisory/ntap-20190213-0001/
https://security.gentoo.org/glsa/201903-16
https://cert-portal.siemens.com/productcert/pdf/ssa-412672.pdf
https://github.com/krlabs/openssh-vulnerabilities
https://github.com/mbadanoiu/MAL-008
https://github.com/Live-Hack-CVE/CVE-2019-6110
https://euvd.enisa.europa.eu/vulnerability/EUVD-2019-15677
https://cvsweb.openbsd.org/src/usr.bin/ssh/scp.c
https://cvsweb.openbsd.org/src/usr.bin/ssh/progressmeter.c
https://cert-portal.siemens.com/productcert/html/ssa-412672.html
https://cert-portal.siemens.com/productcert/html/ssa-398330.html