Cross-Site Scripting (XSS) vulnerability in the RSS Widget of Netgate pfSense Plus (versions 26.03, 25.11.1) and pfSense CE (version 2.8.1) allows remote authenticated attackers to inject arbitrary JavaScript via malicious content in an RSS feed title. The injected script executes in the browser of any authenticated user who views the dashboard, due to insufficient sanitization of feed title data before rendering in the widget.

pfSense Plus before 26.07 and pfSense CE through 2.8.1 contain a stored cross-site scripting vulnerability in the Traffic Graphs top-talkers feature, where PTR records returned by reverse DNS lookups are incorporated without sanitization into AJAX responses and rendered as HTML through a DOM sink in the administrator interface. An attacker who controls a PTR record and generates sufficient traffic to appear as a top talker can execute arbitrary JavaScript in an administrator's browser, gaining access to the authenticated session context and same-origin access to the firewall management interface, enabling account creation and arbitrary OS command execution.

Netgate pfSense CE 2.8.0 allows code execution in the XMLRPC API via pfsense.execphp. NOTE: the Supplier disputes this because the API call is only available to admins and they are intentionally allowed to execute PHP code.

Netgate pfSense CE 2.7.2 allows code execution by using the module installer with a backup file with a serialized PHP object containing the postrebootcommands property. NOTE: the Supplier disputes this because this installer is only available to admins and they are intentionally allowed to execute PHP code.

In pfSense CE /usr/local/www/snort/snortipreputation.php, the value of the iplist parameter is not sanitized of directory traversal-related characters/strings before being used to check if a file exists. While the contents of the file cannot be read, the server reveals whether a file exists, which allows an attacker to enumerate files on the target. The attacker must be authenticated with at least "WebCfg - Services: Snort package" permissions.

Netgate pfSense CE (prior to 2.8.0 beta release) and corresponding Plus builds is vulnerable to Cross-site scripting (XSS) in the Automatic Configuration Backup (ACB) service, allowing remote attackers to execute arbitrary JavaScript, delete backups, or leak sensitive information via an unsanitized "reason" field and a derivable device key generated from the public SSH key.

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.