[arch-security] [ASA-201603-19] dropbear: command injection

[Levente Polyak]

Arch Linux Security Advisory ASA-201603-19
==========================================

Severity: Medium
Date    : 2016-03-14
CVE-ID  : CVE-2016-3116
Package : dropbear
Type    : command injection
Remote  : Yes
Link    : https://wiki.archlinux.org/index.php/CVE

Summary
=======

The package dropbear before version 2016.72-1 is vulnerable to command
injection leading to information disclosure, directory traversal and
possibly other impact.

Resolution
==========

Upgrade to 2016.72-1.

# pacman -Syu "dropbear>=2016.72-1"

The problem has been fixed upstream in version 2016.72.

Workaround
==========

Set X11Forwarding=no in sshd_config. This is the default.
For authorized_keys that specify a "command" restriction, also set the
"restrict" or "no-x11-forwarding" restrictions.

Description
===========

A vulnerability was found in a way dropbear processed X11 forwarding
input. By using a specially crafted request, an attacker could bypass
the authorized_keys command restrictions.

xauth is run under the user's privilege, so this vulnerability offers no
additional access to unrestricted accounts, but could circumvent key or
account restrictions such as sshd_config ForceCommand, authorized_keys
command="..." or restricted shells.

Impact
======

A remote authenticated user who is able to request X11 forwarding can
inject commands leading to information disclosure, directory traversal
and possibly other impact.

References
==========

https://matt.ucc.asn.au/dropbear/CHANGES
https://access.redhat.com/security/cve/CVE-2016-3116

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