Fedora 23 update for openssh, selinux-policy

1) User enumeration via covert timing channel

EUVDB-ID: #VU255

Risk: Medium

CVSSv4.0: 6.9 [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 - Exposure of sensitive information to an unauthorized actor

Exploit availability: Yes

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 updates from vendor's repository.

Vulnerable software versions

Fedora: 23

selinux-policy: before 3.13.1-158.22.fc23

openssh: before 7.2p2-5.fc23

CPE2.3

• cpe:2.3:o:fedoraproject:fedora:23:*:*:*:*:*:*:*
• cpe:2.3:a:fedoraproject:selinux-policy:*:*:*:*:*:fedora:*:*
• cpe:2.3:a:fedoraproject:openssh:*:*:*:*:*:fedora:*:*

External links

https://bodhi.fedoraproject.org/updates/FEDORA-2016-9402100276

Q & A

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.