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Vulnerability of OpenSSH: use after free via ssh-agent

Synthesis of the vulnerability 

An attacker can force the usage of a freed memory area via ssh-agent of OpenSSH, in order to trigger a denial of service, and possibly to run code.
Vulnerable products: OpenBSD, OpenSSH, Ubuntu.
Severity of this weakness: 2/4.
Creation date: 03/03/2021.
Références of this bulletin: CVE-2021-28041, USN-4762-1, VIGILANCE-VUL-34734.

Description of the vulnerability 

An attacker can force the usage of a freed memory area via ssh-agent of OpenSSH, in order to trigger a denial of service, and possibly to run code.
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This security alert impacts software or systems such as OpenBSD, OpenSSH, Ubuntu.

Our Vigil@nce team determined that the severity of this security weakness is medium.

The trust level is of type confirmed by the editor, with an origin of user shell.

An attacker with a expert ability can exploit this security announce.

Solutions for this threat 

OpenSSH: version 8.5.
The version 8.5 is fixed:
  https://www.openssh.com/

OpenBSD: patch for ssh-agent.
A patch is available:
  https://ftp.openbsd.org/pub/OpenBSD/patches/6.7/common/036_sshagent.patch.sig
  https://ftp.openbsd.org/pub/OpenBSD/patches/6.8/common/015_sshagent.patch.sig

Ubuntu: new openssh-client packages.
New packages are available:
  Ubuntu 20.10: openssh-client 1:8.3p1-1ubuntu0.1
  Ubuntu 20.04 LTS: openssh-client 1:8.2p1-4ubuntu0.2
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