SB2019021101 - Debian update for openssh

Description

This security bulletin contains information about 3 secuirty vulnerabilities.

1) Security restrictions bypass (CVE-ID: CVE-2018-20685)

The vulnerability allows a remote attacker to bypass security restrictions on the target system.

The vulnerability exists due to improper validation of filenames by the scp.c source code file in the SCP client . A remote unauthenticated attacker can trick the victim into accessing a file with the filename of . or an empty filename from an attacker-controlled Secure Shell (SSH) server to bypass access restrictions on the system, which could be used to conduct further attacks.

2) Spoofing attack (CVE-ID: CVE-2019-6109)

The vulnerability allows a remote attacker to conduct spoofing attack on the target system.

The weakness exists due to accepting and displaying arbitrary stderr output from the scp server by the scp client. A malicious SCP server can use the object name to manipulate the client output, for example to employ ANSI codes to hide additional files being transferred.

3) Security restrictions bypass (CVE-ID: CVE-2019-6111)

The vulnerability allows a remote attacker to bypass security restrictions on the target system.

The weakness exists due to missing received object name validation by the scp client. A malicious SCP server can overwrite arbitrary files in the SCP client target directory. If a recursive operation (-r) is performed, the server can manipulate subdirectories as well (for example overwrite .ssh/authorized_keys).

Remediation

Install update from vendor's website.

References

• https://www.debian.org/security/2019/dsa-4387