Bug 1537929 (CVE-2016-10708)

Summary: CVE-2016-10708 openssh: Out of sequence NEWKEYS message can allow remote attacker to cause denial of service
Product: [Other] Security Response Reporter: Sam Fowler <sfowler>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED WONTFIX QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: brahma.gdb, carnil, dwalsh, jfch, jjelen, lkundrak, mattias.ellert, pebarbos, plautrba, slawomir, tmraz
Target Milestone: ---Keywords: Reopened, Security
Target Release: ---   
Hardware: All   
OS: Linux   
Fixed In Version: openssh 7.4 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2018-02-06 18:13:50 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Bug Depends On:    
Bug Blocks: 1537930    

Description Sam Fowler 2018-01-24 06:26:23 UTC
sshd in OpenSSH before 7.4 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via an out-of-sequence NEWKEYS message, as demonstrated by Honggfuzz, related to kex.c and packet.c.

External References:

Upstream Patch:

Comment 1 Jakub Jelen 2018-01-24 08:01:03 UTC
OpenSSH 7.4 is in RHEL7.4 so we should be safe here. But the release notes do not talk about this issue:


Are you sure it is denial of service by crashing the whole daemon, or is it just a per-connection process, that is crashing? Are we able to reproduce it?

Comment 2 Salvatore Bonaccorso 2018-01-27 07:40:32 UTC
Hi Jakub,

Regarding the release notes: it is mentioned in the "Bugfixes" section:

 * sshd(8): fix NULL-deref crash if sshd(8) received an out-of-
   sequence NEWKEYS message.

Your second question though is still open.

Comment 3 Pedro Yóssis Silva Barbosa 2018-02-01 19:42:27 UTC
RHEL-6 is affected, RHEL-7 is not.

Although I did not make a reproducer, I made a simple test here (forcing crash in the vulnerable part, through patching the binary with bad opcodes) and could confirm that the DoS is just a per-connection process, not the whole daemon. Hence, WONTFIX.

Comment 7 Pedro Yóssis Silva Barbosa 2018-02-05 13:41:53 UTC

Originally, this issue affected Red Hat Enterprise Linux 7 (version 7.3 and earlier). Due a rebase (RHSA-2017:2029-09), this issue was mitigated in Red Hat Enterprise Linux 7 and later versions.

Comment 9 Pedro Yóssis Silva Barbosa 2018-02-06 18:05:46 UTC

This issue affects the versions of openssh as shipped with Red Hat Enterprise Linux 6 and Red Hat Enterprise Linux 7 (versions 7.3 and earlier).  For Red Hat Enterprise Linux 7 (versions 7.4 and later), this issue was fixed by the Security Advisory RHSA-2017:2029. For Red Hat Enterprise Linux 6, Red Hat Product Security has rated this issue as having Low security impact. A future update may address this issue. For additional information, refer to the Issue Severity Classification: https://access.redhat.com/security/updates/classification/.

Comment 10 Pedro Yóssis Silva Barbosa 2018-02-06 18:10:37 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2017:2029 https://access.redhat.com/errata/RHSA-2017:2029

Comment 11 Brahma 2019-05-15 15:15:35 UTC
Could you please share proposed testcase and reproduction for the same.