User enumeration via covert timing channel in OpenSSH - CVE-2016-6210
Published: August 2, 2016 / Updated: March 20, 2023
Vulnerability identifier: #VU255
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:A/U:Green
CVE-ID: CVE-2016-6210
CWE-ID: CWE-200
Exploitation vector: Remote access
Exploit availability:
Public exploit is available
Vendor: OpenSSH
Affected software:
OpenSSH
OpenSSH
Detailed vulnerability description
The vulnerability allows a remote attacker to enumerate users on system.
The vulnerability exists in most systems where the Blowfish algorithm runs faster than SHA256/SHA512. A remote unauthenticated attacker can determine valid usernames by sending a specially crafted request with a large password (approximately 10,000 characters) to the target ssh daemon. On systems where a valid user's password has been hashed with SHA256/SHA512, the response time will be shorter for a non-existent username than for a valid username.
Successful exploitation of this vulnerability may result in disclosure or user logins.
How to mitigate CVE-2016-6210
Install the latest version of OpenSSH 7.3.