NetSarang Xmanager Enterprise 5.0 Build 1232, Xmanager 5.0 Build 1045, Xshell 5.0 Build 1322, Xftp 5.0 Build 1218, and Xlpd 5.0 Build 1220 contain a malicious nssock2.dll that implements a multi-stage, DNS-based backdoor. The dormant library contacts a C2 DNS server via a specially crafted TXT record for a month‑generated domain. After receiving a decryption key, it then downloads and executes arbitrary code, creates an encrypted virtual file system (VFS) in the registry, and grants the attacker full remote code execution, data exfiltration, and persistence. NetSarang released builds for each product line that remediated the compromise: Xmanager Enterprise Build 1236, Xmanager Build 1049, Xshell Build 1326, Xftp Build 1222, and Xlpd Build 1224. Kaspersky Lab identified an instance of exploitation in the wild in August 2017.

Rejected reason: This CVE ID has been rejected or withdrawn by its CVE Numbering Authority. This vulnerability has been reassigned as CVE-2017-20203 ( https://www.cve.org/CVERecord?id=CVE-2017-20203 ) to have the year of the CVE correspond to the year of public disclosure.

Xftp FTP Client version up to and including 3.0 (build 0238) contain a stack-based buffer overflow vulnerability triggered by a maliciously crafted PWD response from an FTP server. When the client connects to a server and receives an overly long directory string in response to the PWD command, the client fails to properly validate the length of the input before copying it into a fixed-size buffer. This results in memory corruption and allows remote attackers to execute arbitrary code on the client system.

Summary

Terrapin is a prefix truncation attack targeting the SSH protocol. More precisely, Terrapin breaks the integrity of SSH's secure channel. By carefully adjusting the sequence numbers during the handshake, an attacker can remove an arbitrary amount of messages sent by the client or server at the beginning of the secure channel without the client or server noticing it.

Mitigations

To mitigate this protocol vulnerability, OpenSSH suggested a so-called "strict kex" which alters the SSH handshake to ensure a Man-in-the-Middle attacker cannot introduce unauthenticated messages as well as convey sequence number manipulation across handshakes.

Warning: To take effect, both the client and server must support this countermeasure.

As a stop-gap measure, peers may also (temporarily) disable the affected algorithms and use unaffected alternatives like AES-GCM instead until patches are available.

Details

The SSH specifications of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com MACs) are vulnerable against an arbitrary prefix truncation attack (a.k.a. Terrapin attack). This allows for an extension negotiation downgrade by stripping the SSHMSGEXTINFO sent after the first message after SSHMSGNEWKEYS, downgrading security, and disabling attack countermeasures in some versions of OpenSSH. When targeting Encrypt-then-MAC, this attack requires the use of a CBC cipher to be practically exploitable due to the internal workings of the cipher mode. Additionally, this novel attack technique can be used to exploit previously unexploitable implementation flaws in a Man-in-the-Middle scenario.

The attack works by an attacker injecting an arbitrary number of SSHMSGIGNORE messages during the initial key exchange and consequently removing the same number of messages just after the initial key exchange has concluded. This is possible due to missing authentication of the excess SSHMSGIGNORE messages and the fact that the implicit sequence numbers used within the SSH protocol are only checked after the initial key exchange.

In the case of ChaCha20-Poly1305, the attack is guaranteed to work on every connection as this cipher does not maintain an internal state other than the message's sequence number. In the case of Encrypt-Then-MAC, practical exploitation requires the use of a CBC cipher; while theoretical integrity is broken for all ciphers when using this mode, message processing will fail at the application layer for CTR and stream ciphers.

For more details see https://terrapin-attack.com.

Impact

This attack targets the specification of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com), which are widely adopted by well-known SSH implementations and can be considered de-facto standard. These algorithms can be practically exploited; however, in the case of Encrypt-Then-MAC, we additionally require the use of a CBC cipher. As a consequence, this attack works against all well-behaving SSH implementations supporting either of those algorithms and can be used to downgrade (but not fully strip) connection security in case SSH extension negotiation (RFC8308) is supported. The attack may also enable attackers to exploit certain implementation flaws in a man-in-the-middle (MitM) scenario.

XLPD v7.0.0094 and below contains an unquoted service path vulnerability which allows local users to launch processes with elevated privileges.

Xshell v7.0.0099 and below contains a binary hijack vulnerability which allows attackers to execute arbitrary code via a crafted .exe file.

Xmanager v7.0.0096 and below contains a binary hijack vulnerability which allows attackers to execute arbitrary code via a crafted .exe file.

Xlpd v7.0.0094 and below contains a binary hijack vulnerability which allows attackers to execute arbitrary code via a crafted .exe file.

Xftp 7.0.0088p and below contains a binary hijack vulnerability which allows attackers to execute arbitrary code via a crafted .exe file.

Xshell before 7.0.0.76 allows attackers to cause a crash by triggering rapid changes to the title bar.

NetSarang Xshell 7 before Build 0077 includes unintended code strings in paste operations.

NetSarang XFTP Client 6.0149 and earlier version contains a buffer overflow vulnerability caused by improper boundary checks when copying file name from an attacker controlled FTP server. That leads attacker to execute arbitrary code by sending a crafted filename.

NetSarang Xlpd 4 Build 0100 and NetSarang Xmanager Enterprise 4 Build 0186 allow remote attackers to cause a denial of service (daemon crash) via a malformed LPD request.

NetSarang Xlpd 2.1 allows remote attackers to cause a denial of service (crash) via a large number of connections from the same IP address.