Subject: [ASA-202004-11] libssh: denial of service

Arch Linux Security Advisory ASA-202004-11
==========================================

Severity: Medium
Date    : 2020-04-09
CVE-ID  : CVE-2020-1730
Package : libssh
Type    : denial of service
Remote  : Yes
Link    : https://security.archlinux.org/AVG-1130

Summary
=======

The package libssh before version 0.9.4-1 is vulnerable to denial of
service.

Resolution
==========

Upgrade to 0.9.4-1.

# pacman -Syu "libssh>=0.9.4-1"

The problem has been fixed upstream in version 0.9.4.

Workaround
==========

This issue can be mitigated by disabling AES-CTR ciphers.

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

A malicious client or server could crash the counterpart implemented
with libssh before 0.9.4. When AES-CTR ciphers are used and don't get
fully initialized, libssh will crash when it tries to cleanup the AES-
CTR ciphers when closing the connection.

Impact
======

A malicious client or server could crash the counterpart via a crafted
SSH connection.

References
==========

https://www.libssh.org/2020/04/09/libssh-0-9-4-and-libssh-0-8-9-security-release/
https://www.libssh.org/security/advisories/CVE-2020-1730.txt
https://git.libssh.org/projects/libssh.git/commit/?h=stable-0.9&id=958afb1c6ad671fe2a8d671702a88843bb78fc38
https://security.archlinux.org/CVE-2020-1730