Arch Linux Security Advisory ASA-201602-18 ========================================== Severity: High Date : 2016-02-23 CVE-ID : CVE-2016-0739 Package : libssh Type : man-in-the-middle Remote : Yes Link : https://wiki.archlinux.org/index.php/CVE Summary ======= The package libssh before version 0.7.3-1 is vulnerable to man-in-the-middle. Resolution ========== Upgrade to 0.7.3-1. # pacman -Syu "libssh>=0.7.3-1" The problem has been fixed upstream in version 0.7.3. Workaround ========== This issue may be worked around by using other key exchange methods, such as curve25519-sha256@libssh.org or ecdh-sha2-nistp256, both are not vulnerable. By default, an unpatched libssh implementation will already attempt to use these two more secure methods when supported by the other party. Description =========== libssh versions 0.1 and above have a bits/bytes confusion bug and generate the an anormaly 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. Impact ====== A remote attacker can use this flaw to decrypt or intercept SSH sessions. References ========== https://www.libssh.org/2016/02/23/libssh-0-7-3-security-and-bugfix-release/ https://access.redhat.com/security/cve/CVE-2016-0739