FreeBSD : libssh -- weak Diffie-Hellman secret generation (6b3591ea-e2d2-11e5-a6be-5453ed2e2b49)

medium Nessus Plugin ID 89709

Synopsis

The remote FreeBSD host is missing a security-related update.

Description

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.

Solution

Update the affected package.

See Also

https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2016-0739

http://www.nessus.org/u?2a0743a2

http://www.nessus.org/u?caf0f69b

Plugin Details

Severity: Medium

ID: 89709

File Name: freebsd_pkg_6b3591eae2d211e5a6be5453ed2e2b49.nasl

Version: 2.7

Type: local

Published: 3/7/2016

Updated: 1/4/2021

Risk Information

VPR

Risk Factor: Low

Score: 3.6

CVSS v2

Risk Factor: Medium

Base Score: 4.3

Vector: AV:N/AC:M/Au:N/C:P/I:N/A:N

CVSS v3

Risk Factor: Medium

Base Score: 5.9

Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Vulnerability Information

CPE: p-cpe:/a:freebsd:freebsd:libssh, cpe:/o:freebsd:freebsd

Required KB Items: Host/local_checks_enabled, Host/FreeBSD/release, Host/FreeBSD/pkg_info

Patch Publication Date: 3/5/2016

Vulnerability Publication Date: 2/23/2016

Reference Information

CVE: CVE-2016-0739