Information
This variable limits the types of MAC algorithms that SSH can use during communication.
Notes:
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Some organizations may have stricter requirements for approved MACs. Ensure that MACs used are in compliance with site policy
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The only "strong" MACs currently FIPS 140-2 approved are hmac-sha2-256 and hmac-sha2-512
The Supported MACs are:
hmac-md5
hmac-md5-96
hmac-sha1
hmac-sha1-96
hmac-sha2-256
hmac-sha2-512
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
MD5 and 96-bit MAC algorithms are considered weak and have been shown to increase exploitability in SSH downgrade attacks. Weak algorithms continue to have a great deal of attention as a weak spot that can be exploited with expanded computing power. An attacker that breaks the algorithm could take advantage of a MiTM position to decrypt the SSH tunnel and capture credentials and information
Solution
Edit the /etc/ssh/sshd_config file and add/modify the MACs line to contain a comma separated list of the site approved MACs
Example:
MACs [email protected],[email protected],hmac-sha2-512,hmac-sha2-256
Item Details
Category: CONFIGURATION MANAGEMENT, SYSTEM AND SERVICES ACQUISITION
References: 800-53|CM-2, 800-53|CM-6, 800-53|CM-7, 800-53|CM-7(1), 800-53|CM-9, 800-53|SA-3, 800-53|SA-8, 800-53|SA-10, CSCv7|14.4, CSCv7|16.5
Control ID: d927e8ee1a861e70e3ab310c23aa73523e9caaf52836451507634221cf8b82ba