Remote command execution in Dropbear SSH

1) CRLF injection

EUVDB-ID: #VU33987

Risk: Medium

CVSSv3.1: 7.9 [CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:P/RL:O/RC:C]

CVE-ID: CVE-2016-3116

CWE-ID: CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')

Exploit availability: Yes

Description

The vulnerability allows a remote user to bypass implemented security restrictions.

The vulnerability exists due to improper input validation when processing CRLF characters. A remote authenticated user bypass intended shell-command restrictions via crafted X11 forwarding data.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Dropbear: 2013.56 - 2015.71

External links

http://lists.fedoraproject.org/pipermail/package-announce/2016-March/179261.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-March/179269.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-March/179870.html
http://lists.opensuse.org/opensuse-updates/2016-03/msg00105.html
http://lists.opensuse.org/opensuse-updates/2016-03/msg00113.html
http://packetstormsecurity.com/files/136251/Dropbear-SSHD-xauth-Command-Injection-Bypass.html
http://seclists.org/fulldisclosure/2016/Mar/47
http://github.com/tintinweb/pub/tree/master/pocs/cve-2016-3115
http://matt.ucc.asn.au/dropbear/CHANGES
http://security.gentoo.org/glsa/201607-08

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the Internet.

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.