[ASA-201904-11] openssh: multiple issues

[Remi Gacogne]

Arch Linux Security Advisory ASA-201904-11
==========================================

Severity: High
Date    : 2019-04-24
CVE-ID  : CVE-2018-20685 CVE-2019-6109 CVE-2019-6111
Package : openssh
Type    : multiple issues
Remote  : Yes
Link    : https://security.archlinux.org/AVG-951

Summary
=======

The package openssh before version 8.0p1-1 is vulnerable to multiple
issues including insufficient validation, arbitrary file overwrite and
content spoofing.

Resolution
==========

Upgrade to 8.0p1-1.

# pacman -Syu "openssh>=8.0p1-1"

The problems have been fixed upstream in version 8.0p1.

Workaround
==========

None.

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

- CVE-2018-20685 (insufficient validation)

In OpenSSH 7.9, scp.c in the scp client allows remote SSH servers to
bypass intended access restrictions via the filename of . or an empty
filename.

- CVE-2019-6109 (content spoofing)

An issue was discovered in OpenSSH 7.9. Due to missing character
encoding in the progress display, a malicious server (or Man-in-The-
Middle attacker) can employ crafted object names to manipulate the
client output, e.g., by using ANSI control codes to hide additional
files being transferred. This affects refresh_progress_meter() in
progressmeter.c.

- CVE-2019-6111 (arbitrary file overwrite)

An issue was discovered in OpenSSH 7.9. Due to the scp implementation
being derived from 1983 rcp, the server chooses which files/directories
are sent to the client. However, the scp client only performs cursory
validation of the object name returned (only directory traversal
attacks are prevented). A malicious scp server (or Man-in-The-Middle
attacker) can overwrite arbitrary files in the scp client target
directory. If recursive operation (-r) is performed, the server can
manipulate subdirectories as well (for example, to overwrite the
.ssh/authorized_keys file).

Impact
======

A malicious SCP server can overwrite arbitrary files in the scp client
target directory.

References
==========

https://www.openssh.com/txt/release-8.0
https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/scp.c.diff?r1=1.197&r2=1.198&f=h
https://github.com/openssh/openssh-portable/commit/6010c0303a422a9c5fa8860c061bf7105eb7f8b2
https://sintonen.fi/advisories/scp-client-multiple-vulnerabilities.txt
https://github.com/openssh/openssh-portable/commit/8976f1c4b2721c26e878151f52bdf346dfe2d54c
https://github.com/openssh/openssh-portable/commit/391ffc4b9d31fa1f4ad566499fef9176ff8a07dc
https://security.archlinux.org/CVE-2018-20685
https://security.archlinux.org/CVE-2019-6109
https://security.archlinux.org/CVE-2019-6111

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