CVE-2015-5600

Publication date 2 August 2015

Last updated 6 June 2026

Ubuntu priority

Cvss 3 Severity Score

Description

The kbdint_next_device function in auth2-chall.c in sshd in OpenSSH through 6.9 does not properly restrict the processing of keyboard-interactive devices within a single connection, which makes it easier for remote attackers to conduct brute-force attacks or cause a denial of service (CPU consumption) via a long and duplicative list in the ssh -oKbdInteractiveDevices option, as demonstrated by a modified client that provides a different password for each pam element on this list.

Read the notes from the security team

Status

Show unmaintained releases

Package	Ubuntu Release	Status
openssh	15.04 vivid	Fixed 1:6.7p1-5ubuntu1.2
	14.04 LTS trusty	Fixed 1:6.6p1-2ubuntu2.2
	12.04 LTS precise	Fixed 1:5.9p1-5ubuntu1.6

Notes

tyhicks

Only affects systems with KbdInteractiveAuthentication set to 'yes'. By default, that option is set to 'no' in Ubuntu.

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package	Patch details
openssh	Upstream: http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/auth2-chall.c.diff?r1=1.42&r2=1.43&f=h Upstream: 5b64f85

Severity score breakdown

Parameter	Value
Base score	8.1 · High
Attack vector	Network
Attack complexity	High
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	High
Integrity impact	High
Availability impact	High
Vector	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

References

Related Ubuntu Security Notices (USN)

USN-2710-1
OpenSSH vulnerabilities
14 August 2015