CCE-99444-2Platform: cpe:/o:debian:debian_linux:11.x, cpe:/o:ubuntu:ubuntu_linux:20.04, cpe:/o:ubuntu:ubuntu_linux:22.04, cpe:/o:ubuntu:ubuntu_linux:23.04 | Date: (C)2023-02-09 (M)2023-09-01 |
Description:
Key exchange is any method in cryptography by which cryptographic keys are exchanged between two parties, allowing use of a cryptographic algorithm. If the sender and receiver wish to exchange encrypted messages, each must be equipped to encrypt messages to be sent and decrypt messages received
Rationale:
Key exchange methods that are considered weak should be removed. A key exchange method may be weak because too few bits are used, or the hashing algorithm is considered too weak. Using weak algorithms could expose connections to man-in-the-middle attacks
The only Key Exchange Algorithms currently FIPS 140-2 approved are: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256
The Key Exchange algorithms supported by OpenSSH 7 are:
curve25519-sha256
curve25519-sha256@libssh.org
diffie-hellman-group1-sha1
diffie-hellman-group14-sha1
diffie-hellman-group-exchange-sha1
diffie-hellman-group-exchange-sha256
ecdh-sha2-nistp256
ecdh-sha2-nistp384
ecdh-sha2-nistp521
Audit:
Verify that the nosuid option is set if a /tmp partition exists
Run the following command and verify that nothing is returned:
# mount | grep -E \\s/tmp\\s | grep -v nosuid
Remediation:
Edit the /etc/ssh/sshd_config file add/modify the KexAlgorithms line to contain a comma separated list of the site approved key exchange algorithms
KexAlgorithms curve25519-sha256,curve25519-sha256@libssh.org,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256
Notes:
Kex algorithms have a higher preference the earlier they appear in the list
Parameter:
[curve25519-sha256,curve25519-sha256@libssh.org,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256]
Technical Mechanism:
CCSS Severity: | CCSS Metrics: |
CCSS Score : 9.8 | Attack Vector: NETWORK |
Exploit Score: 3.9 | Attack Complexity: LOW |
Impact Score: 5.9 | Privileges Required: NONE |
Severity: CRITICAL | User Interaction: NONE |
Vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H | Scope: UNCHANGED |
| Confidentiality: HIGH |
| Integrity: HIGH |
| Availability: HIGH |
| |
References: Resource Id | Reference |
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SCAP Repo OVAL Definition | oval:org.secpod.oval:def:92353 |
SCAP Repo OVAL Definition | oval:org.secpod.oval:def:89584 |
SCAP Repo OVAL Definition | oval:org.secpod.oval:def:87266 |
SCAP Repo OVAL Definition | oval:org.secpod.oval:def:90440 |