USN-3809-1 fixed vulnerabilities in OpenSSH. The update for CVE-2018-15473
was incomplete and could introduce a regression in certain environments.
This update fixes the problem.
We apologize for the inconvenience.
Original advisory details:
Robert Swiecki discovered that OpenSSH incorrectly handled certain messages.
An attacker could possibly use this issue to cause a denial of service.
This issue only affected Ubuntu 14.04 LTS and Ubuntu 16.04 LTS.
(CVE-2016-10708)
It was discovered that OpenSSH incorrectly handled certain requests.
An attacker could possibly use this issue to access sensitive information.
(CVE-2018-15473)
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).
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.
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. The impact is modifying the permissions of the target directory on the client side.
OpenSSH through 7.7 is prone to a user enumeration vulnerability due to not delaying bailout for an invalid authenticating user until after the packet containing the request has been fully parsed, related to auth2-gss.c, auth2-hostbased.c, and auth2-pubkey.c.
The process_open function in sftp-server.c in OpenSSH before 7.6 does not properly prevent write operations in readonly mode, which allows attackers to create zero-length files.