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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2016.2583 OpenSSH Remote Denial of Service vulnerability 3 November 2016 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: openssh Publisher: FreeBSD Operating System: FreeBSD Impact/Access: Denial of Service -- Remote/Unauthenticated Resolution: Patch/Upgrade CVE Names: CVE-2016-8858 Original Bulletin: https://security.freebsd.org/advisories/FreeBSD-SA-16:33.openssh.asc - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-16:33.openssh Security Advisory The FreeBSD Project Topic: OpenSSH Remote Denial of Service vulnerability Category: contrib Module: OpenSSH Announced: 2016-11-02 Affects: All supported versions of FreeBSD. Corrected: 2016-11-02 06:56:35 UTC (stable/11, 11.0-STABLE) 2016-11-02 07:23:19 UTC (releng/11.0, 11.0-RELEASE-p3) 2016-11-02 06:58:47 UTC (stable/10, 10.3-STABLE) 2016-11-02 07:23:36 UTC (releng/10.3, 10.3-RELEASE-p12) CVE Name: CVE-2016-8858 For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>. I. Background OpenSSH is an implementation of the SSH protocol suite, providing an encrypted and authenticated transport for a variety of services, including remote shell access. During the SSH handshake procedure, the client and server exchanges the supported encryption, MAC and compression algorithms along with other information to negotiate algorithms for initial key exchange, with a message named SSH_MSG_KEXINIT. II. Problem Description When processing the SSH_MSG_KEXINIT message, the server could allocate up to a few hundreds of megabytes of memory per each connection, before any authentication take place. III. Impact A remote attacker may be able to cause a SSH server to allocate an excessive amount of memory. Note that the default MaxStartups setting on FreeBSD will limit the effectiveness of this attack. IV. Workaround No workaround is available, but systems where sshd(8) is not used are not vulnerable. V. Solution Perform one of the following: 1) Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date. The sshd(8) service has to be restarted after the update. A reboot is recommended but not required. 2) To update your vulnerable system via a binary patch: Systems running a RELEASE version of FreeBSD on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility: # freebsd-update fetch # freebsd-update install The sshd(8) service has to be restarted after the update. A reboot is recommended but not required. 3) To update your vulnerable system via a source code patch: The following patches have been verified to apply to the applicable FreeBSD release branches. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. # fetch https://security.FreeBSD.org/patches/SA-16:33/openssh.patch # fetch https://security.FreeBSD.org/patches/SA-16:33/openssh.patch.asc # gpg --verify openssh.patch.asc b) Apply the patch. Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile the operating system using buildworld and installworld as described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>. The sshd(8) service has to be restarted after the update. A reboot is recommended but not required. VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - - ------------------------------------------------------------------------- stable/10/ r308199 releng/10.3/ r308203 stable/11/ r308198 releng/11.0/ r308202 - - ------------------------------------------------------------------------- To see which files were modified by a particular revision, run the following command, replacing NNNNNN with the revision number, on a machine with Subversion installed: # svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base Or visit the following URL, replacing NNNNNN with the revision number: <URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN> VII. References <URL:http://seclists.org/oss-sec/2016/q4/195> <URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-8858> The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:33.openssh.asc> - -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.1.15 (FreeBSD) iQIcBAEBCgAGBQJYGZhkAAoJEO1n7NZdz2rnws4P/0i2V2lw3snDi4oVsX2AVkl+ bQ9iRUvgO0SSB4b8JZ8dK6wws8InDR8oihm8jBsaOYPOxu7Wz9Zua2ZAjBAY/GLB o2+2UMGKVNlP59D/pwBD3qWEjG2KYpE5hItX7iykjwDvd8c7UOLZt7oofVfq8R7D 84BkMQb9DM/1PwFI+ztMYN3uAlzsNxi0GqoHe7PBYmA5rq3QF9LoUlRyOW9KQq8Q TsBg8briGhy44XifhxU7eUsPUrxJLb5c/w3xsuzSw1AFpgSAc8IKAcrknnTdy+0c k5GfJz/84xcN1/HO6FDVtYgIoOK2C/ljCHiRAPRsVK3TvXl6agErVBf3CTvWKjg9 NY6QD0KTJw5QF0LT6GbLRAdwnAexQI0U7Hw3Xylv2CFnaxsdYeB9YTVqqMricUqQ 7GZ/ktiXJwBpDLkaieeI6WhbAVdsNQc5A1UWQwjv6mFr5TKhOFWvmHRo/KZprWqd vFqYNHc3NngcKs537WOXchNnW46hWMsiis/1mJfiRZd89rzq5Dtz7tCcX1c7RgRW 4h0vhtqRMQraby0fI0ND3kC7EnXchMqWAoQ3Tric+2yWQMW/OGDvWXWbM0HqUKq7 7fOGMmXmLhQnkykf4uwjrP4cyMSzSbGdrLQxpwWPwZoH47es/qYKHukBRcnmEkA+ VpT6Vpm0Lqi80W5bh783 =xyal - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/render.html?cid=1980 =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). 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