This Metasploit module uses a malformed packet or timing attack to enumerate users on an OpenSSH server. The default action sends a malformed (corrupted) SSH_MSG_USERAUTH_REQUEST packet using public key authentication (must be enabled) to enumerate users. On some versions of OpenSSH under some configurations, OpenSSH will return a "permission denied" error for an invalid user faster than for a valid user, creating an opportunity for a timing attack to enumerate users. Testing note: invalid users were logged, while valid users were not. YMMV.
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Red Hat Security Advisory 2017-2563-01 - OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server. Security Fix: A covert timing channel flaw was found in the way OpenSSH handled authentication of non-existent users. A remote unauthenticated attacker could possibly use this flaw to determine valid user names by measuring the timing of server responses.
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Red Hat Security Advisory 2017-2029-01 - OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server. The following packages have been upgraded to a later upstream version: openssh. Security Fix: A covert timing channel flaw was found in the way OpenSSH handled authentication of non-existent users. A remote unauthenticated attacker could possibly use this flaw to determine valid user names by measuring the timing of server responses.
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Gentoo Linux Security Advisory 201612-18 - Multiple vulnerabilities have been found in OpenSSH, the worst of which allows remote attackers to cause Denial of Service. Versions less than 7.3_p1-r7 are affected.
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Ubuntu Security Notice 3061-1 - Eddie Harari discovered that OpenSSH incorrectly handled password hashing when authenticating non-existing users. A remote attacker could perform a timing attack and enumerate valid users. Tomas Kuthan, Andres Rojas, and Javier Nieto discovered that OpenSSH did not limit password lengths. A remote attacker could use this issue to cause OpenSSH to consume resources, leading to a denial of service. Various other issues were also addressed.
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Slackware Security Advisory - New openssh packages are available for Slackware 13.0, 13.1, 13.37, 14.0, 14.1, 14.2, and -current to fix security issues.
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This is a Linux/portable port of OpenBSD's excellent OpenSSH. OpenSSH is based on the last free version of Tatu Ylonen's SSH with all patent-encumbered algorithms removed, all known security bugs fixed, new features reintroduced, and many other clean-ups.
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Debian Linux Security Advisory 3626-1 - Eddie Harari reported that the OpenSSH SSH daemon allows user enumeration through timing differences when trying to authenticate users. When sshd tries to authenticate a non-existing user, it will pick up a fixed fake password structure with a hash based on the Blowfish algorithm. If real users passwords are hashed using SHA256/SHA512, then a remote attacker can take advantage of this flaw by sending large passwords, receiving shorter response times from the server for non-existing users.
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OpenSSHD versions 7.2p2 and below user enumeration exploit.
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