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Category:   Application (VPN)  >   OpenSSH Vendors:
(Oracle Issues Fix for Oracle Linux) OpenSSH 'KbdInteractiveDevices' Lets Remote Users Bypass Security Restrictions on the Target System
SecurityTracker Alert ID:  1034223
SecurityTracker URL:
CVE Reference:   CVE-2015-5600   (Links to External Site)
Date:  Nov 24 2015
Impact:   Host/resource access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  

Description:   A vulnerability was reported in OpenSSH. A remote user can bypass authentication attempt limits on the target system.

A remote user can request the keyboard-interactive authentication option ('KbdInteractiveDevices') to open a large number of keyboard-interactive devices on the target server and perform a brute-force password guessing attack against the target sshd service. The number of password attempts can effectively exceed the 'MaxAuthTries' limit and are permitted to occur until the 'LoginGraceTime' limit is reached or the number of keyboard-interactive devices are used.

Servers that have keyboard-interactive authentication enabled (e.g., FreeBSD in the default configuration) are affected.

A demonstration exploit command is provided:

ssh -l[username] -oKbdInteractiveDevices=`perl -e 'print "pam," x 10000'` [target]

The original advisory is available at:

kingcope reported this vulnerability.

Impact:   A remote user can bypass authentication attempt limits on the target system.
Solution:   Oracle has issued a fix.

The Oracle Linux advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Access control error, State error
Underlying OS:  Linux (Oracle)
Underlying OS Comments:  7

Message History:   This archive entry is a follow-up to the message listed below.
Jul 20 2015 OpenSSH 'KbdInteractiveDevices' Lets Remote Users Bypass Security Restrictions on the Target System

 Source Message Contents

Subject:  [El-errata] ELSA-2015-2088 Moderate: Oracle Linux 7 openssh security, bug fix, and enhancement update

Oracle Linux Security Advisory ELSA-2015-2088

The following updated rpms for Oracle Linux 7 have been uploaded to the 
Unbreakable Linux Network:



Description of changes:

- Use the correct constant for glob limits (#1160377)

- Extend memory limit for remote glob in sftp acc. to stat limit (#1160377)

- Fix vulnerabilities published with openssh-7.0 (#1265807)
  - Privilege separation weakness related to PAM support
  - Use-after-free bug related to PAM support

- Increase limit of files for glob match in sftp to 8192 (#1160377)

- Add GSSAPIKexAlgorithms option for server and client application 

- Security fixes released with openssh-6.9 (CVE-2015-5352) (#1247864)
  - XSECURITY restrictions bypass under certain conditions in ssh(1) 
  - weakness of agent locking (ssh-add -x) to password guessing (#1238238)

- only query each keyboard-interactive device once (CVE-2015-5600) 

- One more typo in manual page documenting TERM variable (#1162683)
- Fix race condition with auditing messages answers (#1240613)

- Fix ldif schema to have correct spacing on newlines (#1184938)
- Add missing values for sshd test mode (#1187597)
- ssh-copy-id: tcsh doesnt work with multiline strings (#1201758)
- Fix memory problems with newkeys and array transfers (#1223218)
- Enhance AllowGroups documentation in man page (#1150007)

- Increase limit of files for glob match in sftp (#1160377)
- Add to /etc/pam.d/sshd (#1204233)
- Show all config values in sshd test mode (#1187597)
- Document required selinux boolean for working ssh-ldap-helper (#1178116)
- Consistent usage of pam_namespace in sshd (#1125110)
- Fix auditing when using combination of ForcedCommand and PTY (#1199112)
- Add sftp option to force mode of created files (#1197989)
- Ability to specify an arbitrary LDAP filter in ldap.conf for 
ssh-ldap-helper (#1201753)
- Provide documentation line for systemd service and socket (#1181591)
- Provide LDIF version of LPK schema (#1184938)
- Document TERM environment variable (#1162683)
- Fix ssh-copy-id on non-sh remote shells (#1201758)
- Do not read RSA1 hostkeys for HostBased authentication in FIPS (#1197666)

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