Vulnerability identifier: #VU255
Vulnerability risk: Medium
CVSSv3.1: 4.9 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:F/RL:O/RC:C]
CVE-ID:
CWE-ID:
CWE-200
Exploitation vector: Network
Exploit availability: Yes
Vulnerable software:
OpenSSH
Server applications /
Remote management servers, RDP, SSH
Vendor: OpenSSH
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.
Mitigation
Install the latest version of OpenSSH 7.3.
Vulnerable software versions
OpenSSH: 6.0p1 - 7.2p2
External links
http://www.openssh.com/txt/release-7.3
Can this vulnerability be exploited remotely?
Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.
Is there known malware, which exploits this vulnerability?
No. We are not aware of malware exploiting this vulnerability. However, a fully functional exploit for this vulnerability is available.