Security Bulletin
Summary
The Logjam Attack on TLS connections using the Diffie-Hellman (DH) key exchange protocol affects IBM GPFS for Windows V3.5
Vulnerability Details
CVEID: CVE-2015-4000
DESCRIPTION: The TLS protocol could allow a remote attacker to obtain sensitive information, caused by the failure to properly convey a DHE_EXPORT ciphersuite choice. An attacker could exploit this vulnerability using man-in-the-middle techniques to force a downgrade to 512-bit export-grade cipher. Successful exploitation could allow an attacker to recover the session key as well as modify the contents of the traffic. This vulnerability is commonly referred to as "Logjam".
CVSS Base Score: 4.3
CVSS Temporal Score: See https://exchange.xforce.ibmcloud.com/vulnerabilities/103294 for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (AV:N/AC:M/Au:N/C:P/I:N/A:N)
Affected Products and Versions
OpenSSH for GPFS V3.5 for Windows
Remediation/Fixes
None
Workarounds and Mitigations
On the Windows node running GPFS V3.5, login with Administrator privileges and perform the following steps from an elevated SUA Korn Shell (ksh):
1. Issue the commands:
awk '{ if ($5 <= 2000) printf "#"; print }' /usr/lpp/mmfs/platform/etc/moduli > /tmp/large_moduli
cp /tmp/large_moduli /usr/lpp/mmfs/platform/etc/moduli
cp /tmp/large_moduli /usr/local/etc/moduli
2. Edit the file /usr/local/etc/sshd_config and append the following line at the end. Make sure that all algorithm names are comma separated in a single line, without any intervening spaces or tabs.
KexAlgorithms
curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group14-sha1,diffie-hellman-gr
oup-exchange-sha1,diffie-hellman-group-exchange-sha256
3. Edit the file /usr/local/etc/ssh_config and append the following line at the end. Make sure that all algorithm names are comma separated in a single line, without any intervening spaces or tabs.
KexAlgorithms
curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group14-sha1
4. To generate any missing keys, issue:
/usr/lpp/mmfs/platform/bin/ssh-keygen -A
5. To verify the configuration files, issue:
/usr/lpp/mmfs/platform/sbin/sshd -T
Make sure that there are no error messages and that kexalgorithms matches as specified in (2).
6. Restart the sshd daemon or reboot the node so that the modified configuration takes effect.
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References
Acknowledgement
Reported to IBM by The WeakDH team at https://weakdh.org
*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.
Disclaimer
Review the IBM security bulletin disclaimer and definitions regarding your responsibilities for assessing potential impact of security vulnerabilities to your environment.
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Document Information
Modified date:
25 June 2021
UID
isg3T1022361