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AUSCERT External Security Bulletin Redistribution
ESB-2024.0574
2024-01 Reference Advisory: Junos OS and Junos OS Evolved:
Impact of Terrapin SSH Attack (CVE-2023-48795)
29 January 2024
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AusCERT Security Bulletin Summary
---------------------------------
Product: Junos OS and Junos OS Evolved
Publisher: Juniper Networks
Operating System: Juniper
Resolution: Patch/Upgrade
CVE Names: CVE-2023-48795
Original Bulletin:
https://supportportal.juniper.net/s/article/2024-01-Reference-Advisory-Junos-OS-and-Junos-OS-Evolved-Impact-of-Terrapin-SSH-Attack-CVE-2023-48795
Comment: CVSS (Max): 3.7 CVE-2023-48795 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N)
CVSS Source: Juniper Networks
Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
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Article ID: JSA76462
Product Affected: This issue affects all versions of Junos OS and Junos OS
Evolved with the ChaCha20-poly1305 SSH cipher enabled.
Severity Level: Low
CVSS Score: 3.7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N)
Problem:
An Improper Validation of Integrity Check Value vulnerability in OpenSSH before
9.6 of Juniper Networks Junos OS and Junos OS Evolved allows a remote attacker
to bypass integrity checks such that some packets are omitted (from the
extension negotiation message), and a client and server may consequently end up
with a connection for which some security features have been downgraded or
disabled, aka the Terrapin Attack.
The most serious identified impact is that it lets an on-path attacker delete
the SSH2_MSG_EXT_INFO message sent before authentication starts, allowing the
attacker to disable a subset of the keystroke timing obfuscation features
introduced in OpenSSH 9.5. There is no other discernable impact to session
secrecy or session integrity.
Since we do not use OpenSSH 9.5 in Junos OS or Junos OS Evolved, the impact of
this issue is limited to a stuck connection in the initial handshake stage.
Therefore, it is not as severe as the issue seen in OpenSSH 9.5
Note: This issue is only affected when an on-path attacker at the network layer
intercepts and modifies the handshake exchange, and the connection is secured
by either ChaCha20-Poly1305 or CBC with Encrypt-then-MAC.
Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
This issue was discovered during external security research.
This issue has been assigned CVE-2023-48795 .
Solution:
This issue can be completely remediated by excluding the chacha20-poly1305
cipher from SSH and configuring the following ciphers for SSH:
user@junos# set system services ssh ciphers [aes128-gcm@openssh.com
aes256-gcm@openssh.com]
The chacha20-poly1305 cipher has been hidden and deprecated in the following
releases:
Junos OS: 19.4R3-S13, 20.4R3-S10, 21.4R3-S6, 22.1R3-S5, 22.2R3-S3, 22.4R3-S1,
23.2R2, 23.4R2, 24.1R1, and all subsequent releases.
Junos OS Evolved: 19.4R3-S13, 20.4R3-S10, 21.4R3-S6, 22.1R3-S5, 22.2R3-S3,
22.4R3-S1, 23.2R2, 23.4R2, 24.1R1, and all subsequent releases.
This issue is being tracked as PR 1781732 which is visible on the Customer
Support website.
Note: Juniper SIRT's policy is not to evaluate releases which are beyond End of
Engineering (EOE) or End of Life (EOL).
Workaround:
See Solution section above for effective mitigation techniques.
Modification History:
o 2024-01-25: Initial Publication.
Related Information:
o KB16613: Overview of the Juniper Networks SIRT Quarterly Security Bulletin
Publication Process
o KB16765: In which releases are vulnerabilities fixed?
o KB16446: Common Vulnerability Scoring System (CVSS) and Juniper's Security
Advisories
o Report a Security Vulnerability - How to Contact the Juniper Networks
Security Incident Response Team
o CVE-2023-48795 at cve.mitre.org
Acknowledgements
o Researchers from the Ruhr University Bochum developed the Terrapin attack
and also discovered exploitable implementation flaws in AsyncSSH.
o Terrapin Attack: Breaking SSH Channel Integrity By Sequence Number
Manipulation, Fabian Baumer, Marcus Brinkmann, Jorg Schwenk.
Last Updated: 2024-01-25
Created: 2024-01-25
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