A default RHEL 8/9 system is going to use the system-wide crypto
policies per /etc/sysconfig/sshd. Below is just a summarized version of
https://access.redhat.com/security/cve/cve-2023-48795
We can add in a cryptop-policies sub policy by creating the following file:
cat << EOF > /etc/crypto-policies/policies/modules/CVE-2023-48795.pmod
cipher@SSH = -CHACHA20-POLY1305
ssh_etm = 0
EOF
Append this crypto policy to your current system crypto policies:
update-crypto-policies --set $(update-crypto-policies --show):CVE-2023-48795
Verify the new policy has taken place:
update-crypto-policies --show
Restart the application as recommended by command output:
systemctl restart sshd.service
Thanks,
Jacob
On 1/23/2024 11:02 AM, Kaushal Shriyan wrote:
Hi,
I have the SSH Terrapin Prefix Truncation Weakness on Red Hat Enterprise
Linux release 8.7 (Ootpa). The details are as follows.
# rpm -qa | grep openssh
openssh-8.0p1-16.el8.x86_64
openssh-askpass-8.0p1-16.el8.x86_64
openssh-server-8.0p1-16.el8.x86_64
openssh-clients-8.0p1-16.el8.x86_64
# cat /etc/redhat-release
Red Hat Enterprise Linux release 8.7 (Ootpa)
#
SSH Terrapin Prefix Truncation Weakness (CVE-2023-48795)
Synopsis
The remote SSH server is vulnerable to a mitm prefix truncation attack.
Description
The remote SSH server is vulnerable to a man-in-the-middle prefix
truncation weakness known as Terrapin.
This can allow a remote, man-in-the-middle attacker to bypass integrity
checks and downgrade the
connection's security.
Note that this plugin only checks for remote SSH servers that support
either ChaCha20-Poly1305 or CBC
with Encrypt-then-MAC and do not support the strict key exchange
countermeasures. It does not check for
vulnerable software versions.
See Also
https://terrapin-attack.com/ <https://terrapin-attack.com/>
Solution
Contact the vendor for an update with the strict key exchange
countermeasures or disable the affected
algorithms.
Risk Factor
Medium
CVSS v3.0 Base Score
5.9 (CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N)
CVSS v3.0 Temporal Score
5.3 (CVSS:3.0/E:P/RL:O/RC:C)
VPR Score
6.9
CVSS v2.0 Base Score
5.4 (CVSS2#AV:N/AC:H/Au:N/C:N/I:C/A:N)
CVSS v2.0 Temporal Score
4.2 (CVSS2#E:POC/RL:OF/RC:C)
187315 (10) - SSH Terrapin Prefix Truncation Weakness (CVE-2023-48795) 16
References
CVE CVE-2023-48795
Is there a way to configure /etc/ssh/sshd_config to mitigate SSH
Terrapin Prefix Truncation Weakness (CVE-2023-48795)
Please guide me.
Thanks in advance.
Best Regards,
Kaushal
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