libssh before 0.7.3 improperly truncates ephemeral secrets generated for the (1) diffie-hellman-group1 and (2) diffie-hellman-group14 key exchange methods to 128 bits, which makes it easier for man-in-the-middle attackers to decrypt or intercept SSH sessions via unspecified vectors, aka a 'bits/bytes confusion bug.' (CVE-2016-0739)

The remote Ubuntu 14.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-2912-1 advisory.

    Mariusz Ziulek discovered that libssh incorrectly handled certain packets. A remote attacker could     possibly use this issue to cause libssh to crash, resulting in a denial of service. (CVE-2015-3146)

    Aris Adamantiadis discovered that libssh incorrectly generated ephemeral secret keys of 128 bits instead     of the recommended 1024 or 2048 bits when using the diffie-hellman-group1 and diffie-hellman-group14     methods. If a remote attacker were able to perform a machine-in-the-middle attack, this flaw could be     exploited to view sensitive information. (CVE-2016-0739)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Fix CVE-2016-0739

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

This update for libssh fixes the following issues :

  - CVE-2016-0739: Fix Weakness in diffie-hellman secret key     generation. (bsc#965875)

Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

Andreas Schneider reports :

libssh versions 0.1 and above have a bits/bytes confusion bug and generate an abnormally short ephemeral secret for the diffie-hellman-group1 and diffie-hellman-group14 key exchange methods.
The resulting secret is 128 bits long, instead of the recommended sizes of 1024 and 2048 bits respectively. There are practical algorithms (Baby steps/Giant steps, Pollard's rho) that can solve this problem in O(2^63) operations.

Both client and server are are vulnerable, pre-authentication. This vulnerability could be exploited by an eavesdropper with enough resources to decrypt or intercept SSH sessions. The bug was found during an internal code review by Aris Adamantiadis of the libssh team.

The remote Redhat Enterprise Linux 7 host has packages installed that are affected by a vulnerability as referenced in the RHSA-2016:0566 advisory.

    libssh is a library which implements the SSH protocol. It can be used to implement client and server     applications.

    Security Fix(es):

    * A type confusion issue was found in the way libssh generated ephemeral secrets for the diffie-hellman-     group1 and diffie-hellman-group14 key exchange methods. This would cause an SSHv2 Diffie-Hellman handshake     to use significantly less secure random parameters. (CVE-2016-0739)

    Red Hat would like to thank Aris Adamantiadis for reporting this issue.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The remote host is affected by the vulnerability described in GLSA-201606-12 (libssh and libssh2: Multiple vulnerabilities)

    libssh and libssh2 both have a bits/bytes confusion bug and generate an       abnormaly short ephemeral secret for the diffie-hellman-group1 and       diffie-hellman-group14 key exchange methods. The resulting secret is 128       bits long, instead of the recommended sizes of 1024 and 2048 bits       respectively.
    Additionally, a double free on dangling pointers in initial key exchange       packets within libssh could leave dangling pointers in the session crypto       structures. It is possible to send a malicious kexinit package to       eventually cause a server to do a double-free before this fix. This could       be used for a Denial of Service attack.
  Impact :

    Remote attackers may gain access to confidential information due to the       short keysize generated by libssh and libssh2, or cause a Denial of       Service condition.
  Workaround :

    There is no known workaround at this time.

According to its self-reported version, the Tenable SecurityCenter application installed on the remote host is prior to 5.4.0. It is, therefore, affected by multiple vulnerabilities :

  - An arbitrary code execution vulnerability exists in the     bundled version of libcurl due to using an insecure path     to look for specific libraries, including the current     working directory, which may not be under user control.
    A remote attacker can exploit this to inject and execute     arbitrary code in the context of the current user.
    (CVE-2016-4802)

  - Multiple flaws exist in the bundled version of libssh     due to a failure to securely generate Diffie-Hellman     secret keys. A man-in-the-middle attacker can exploit     these flaws to intercept and decrypt SSH sessions.
    (CVE-2016-0739, CVE-2016-0787)

  - An integer overflow condition exists in the bundled     version of libcurl due to improper validation of     user-supplied input when handling 'timeval'. An attacker     can exploit this to have an unspecified impact.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

ID	名称	产品	系列	发布时间	最近更新时间	严重程度
93750	F5 Networks BIG-IP : libssh vulnerability (K57255643)	Nessus	F5 Networks Local Security Checks	2016/9/28	2026/1/23	medium
88930	Ubuntu 14.04 LTS : libssh vulnerabilities (USN-2912-1)	Nessus	Ubuntu Local Security Checks	2016/2/24	2025/2/18	high
89621	Fedora 23 : libssh-0.7.3-1.fc23 (2016-d9f950c779)	Nessus	Fedora Local Security Checks	2016/3/4	2021/1/11	medium
89654	SUSE SLED11 Security Update : libssh (SUSE-SU-2016:0622-1)	Nessus	SuSE Local Security Checks	2016/3/4	2021/1/6	medium
89656	SUSE SLED12 Security Update : libssh (SUSE-SU-2016:0625-1)	Nessus	SuSE Local Security Checks	2016/3/4	2021/1/6	medium
89709	FreeBSD : libssh -- weak Diffie-Hellman secret generation (6b3591ea-e2d2-11e5-a6be-5453ed2e2b49)	Nessus	FreeBSD Local Security Checks	2016/3/7	2021/1/4	medium
89890	Fedora 22 : libssh-0.7.3-1.fc22 (2016-dc9e8da03c)	Nessus	Fedora Local Security Checks	2016/3/14	2021/1/11	medium
90302	RHEL 7 : libssh (RHSA-2016:0566)	Nessus	Red Hat Local Security Checks	2016/4/1	2025/4/15	medium
91843	GLSA-201606-12 : libssh and libssh2: Multiple vulnerabilities	Nessus	Gentoo Local Security Checks	2016/6/27	2021/1/11	medium
92558	Tenable SecurityCenter < 5.4.0 Multiple Vulnerabilities (TNS-2016-12)	Nessus	Misc.	2016/7/26	2020/10/9	high

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