Edge SWG (formerly ProxySG) vulnerability status in respect to CVE-2023-48795
Article ID: 277886
Updated On:
Products
ISG Proxy
SWG VA-100
ProxySG Software - SGOS
Advanced Secure Gateway Software - ASG
ASG-S200
ASG-S400
ASG-S500
Issue/Introduction
Proxy administrators would like to determine if Edge SWG (formerly ProxySG) devices are vulnerable to CVE-2023-48795.
Environment
Edge SWG (formerly ProxySG)
Cause
Vulnerability Details
- CVE ID Number: CVE-2023-48795
- Component: OpenSSH
- Date Published: December 18th, 2023
- Description: The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6 and other products, allows remote attackers 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 a Terrapin attack. This occurs because the SSH Binary Packet Protocol (BPP), implemented by these extensions, mishandles the handshake phase and mishandles use of sequence numbers. For example, there is an effective attack against SSH's use of ChaCha20-Poly1305 (and CBC with Encrypt-then-MAC). The bypass occurs in [email protected] and (if CBC is used) the [email protected] MAC algorithms. This also affects Maverick Synergy Java SSH API before 3.1.0-SNAPSHOT, Dropbear through 2022.83, Ssh before 5.1.1 in Erlang/OTP, PuTTY before 0.80, AsyncSSH before 2.14.2, golang.org/x/crypto before 0.17.0, libssh before 0.10.6, libssh2 through 1.11.0, Thorn Tech SFTP Gateway before 3.4.6, Tera Term before 5.1, Paramiko before 3.4.0, jsch before 0.2.15, SFTPGo before 2.5.6, Netgate pfSense Plus through 23.09.1, Netgate pfSense CE through 2.7.2, HPN-SSH through 18.2.0, ProFTPD before 1.3.8b (and before 1.3.9rc2), ORYX CycloneSSH before 2.3.4, NetSarang XShell 7 before Build 0144, CrushFTP before 10.6.0, ConnectBot SSH library before 2.2.22, Apache MINA sshd through 2.11.0, sshj through 0.37.0, TinySSH through 20230101, trilead-ssh2 6401, LANCOM LCOS and LANconfig, FileZilla before 3.66.4, Nova before 11.8, PKIX-SSH before 14.4, SecureCRT before 9.4.3, Transmit5 before 5.10.4, Win32-OpenSSH before 9.5.0.0p1-Beta, WinSCP before 6.2.2, Bitvise SSH Server before 9.32, Bitvise SSH Client before 9.33, KiTTY through 0.76.1.13, the net-ssh gem 7.2.0 for Ruby, the mscdex ssh2 module before 1.15.0 for Node.js, the thrussh library before 0.35.1 for Rust, and the Russh crate before 0.40.2 for Rust.
- Vector Assessment: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
- Base Score: 5.9 (Medium)
Advisory Link(s)
Resolution
For impacted Edge SWG (formerly ProxySG) devices, you can manually disable the affected cipher and HMACS. This consists of removing the ChaCha20 cipher and ETM HMACs via the appliance CLI.
Commands are as follows:
#(config ssh-console)ciphers remove [email protected] #(config ssh-console)hmacs remove [email protected] #(config ssh-console)hmacs remove [email protected] #(config ssh-console)hmacs remove [email protected] #(config ssh-console)hmacs remove [email protected],[email protected] #(config ssh-console)hmacs remove hmac-sha2-256 #(config ssh-console)hmacs remove hmac-sha1 #(config ssh-console)hmacs remove [email protected] #(config ssh-console)hmacs remove [email protected] #(config ssh-console)hmacs remove [email protected] #(config ssh-console)hmacs remove [email protected]
The other alternative is to force the use of GCM ciphers (which effectively removes ChaCha20 cipher and removes all CBC ciphers (which pair with ETM HMACS to produce the vulnerability). Depending on the interoperability required, this may be the preferred approach.
#(config ssh-console)ciphers set [email protected],[email protected]
The same steps are to be repeated for the SSH Client:
#(config ssh-client)
Additional Information
- SGOS 7.3.x and 7.4.x have the same set of ciphers and HMACS.
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