OpenSSH 7.7 through 7.9 and 8.x before 8.1, when compiled with an experimental key type, has a pre-authentication integer overflow if a client or server is configured to use a crafted XMSS key. This leads to memory corruption and remote code execution because of an error in the XMSS key parsing algorithm. NOTE: the XMSS implementation is considered experimental in all released OpenSSH versions, and there is no supported way to enable it when building portable OpenSSH.

References

• https://nvd.nist.gov/vuln/detail/CVE-2019-16905
• https://0day.life/exploits/0day-1009.html
• https://bugzilla.suse.com/show_bug.cgi?id=1153537
• https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/sshkey-xmss.c
• https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/sshkey-xmss.c.diff?r1=1.5&r2=1.6&f=h
• https://security.gentoo.org/glsa/201911-01
• https://security.netapp.com/advisory/ntap-20191024-0003/
• https://ssd-disclosure.com/archives/4033/ssd-advisory-openssh-pre-auth-xmss-integer-overflow
• https://www.openssh.com/releasenotes.html
• https://www.openwall.com/lists/oss-security/2019/10/09/1
• https://cert-portal.siemens.com/productcert/pdf/ssa-412672.pdf