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.

A PAN-OS URL filtering policy misconfiguration could allow a network-based attacker to conduct reflected and amplified TCP denial-of-service (RDoS) attacks. The DoS attack would appear to originate from a Palo Alto Networks PA-Series (hardware), VM-Series (virtual) and CN-Series (container) firewall against an attacker-specified target. To be misused by an external attacker, the firewall configuration must have a URL filtering profile with one or more blocked categories assigned to a source zone that has an external facing interface. This configuration is not typical for URL filtering and, if set, is likely unintended by the administrator. If exploited, this issue would not impact the confidentiality, integrity, or availability of our products. However, the resulting denial-of-service (DoS) attack may help obfuscate the identity of the attacker and implicate the firewall as the source of the attack. We have taken prompt action to address this issue in our PAN-OS software. All software updates for this issue are expected to be released no later than the week of August 15, 2022. This issue does not impact Panorama M-Series or Panorama virtual appliances. This issue has been resolved for all Cloud NGFW and Prisma Access customers and no additional action is required from them.

An OS command injection vulnerability in the Palo Alto Networks PAN-OS web interface enables an authenticated administrator to execute arbitrary OS commands to escalate privileges. This issue impacts: PAN-OS 9.0 version 9.0.10 through PAN-OS 9.0.14; PAN-OS 9.1 version 9.1.4 through PAN-OS 9.1.10; PAN-OS 10.0 version 10.0.7 and earlier PAN-OS 10.0 versions; PAN-OS 10.1 version 10.1.0 through PAN-OS 10.1.1. Prisma Access firewalls and firewalls running PAN-OS 8.1 versions are not impacted by this issue.

A reflected cross-site scripting (XSS) vulnerability in the Palo Alto Network PAN-OS web interface enables an authenticated network-based attacker to mislead another authenticated PAN-OS administrator to click on a specially crafted link that performs arbitrary actions in the PAN-OS web interface as the targeted authenticated administrator. This issue impacts: PAN-OS 8.1 versions earlier than 8.1.20; PAN-OS 9.0 versions earlier than 9.0.14; PAN-OS 9.1 versions earlier than 9.1.10; PAN-OS 10.0 versions earlier than 10.0.2. This issue does not affect Prisma Access.

An improper restriction of XML external entity (XXE) reference vulnerability in the Palo Alto Networks PAN-OS web interface enables an authenticated administrator to read any arbitrary file from the file system and send a specifically crafted request to the firewall that causes the service to crash. Repeated attempts to send this request result in denial of service to all PAN-OS services by restarting the device and putting it into maintenance mode. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.20; PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.10; PAN-OS 10.0 versions earlier than PAN-OS 10.0.6. This issue does not affect Prisma Access.

A time-of-check to time-of-use (TOCTOU) race condition vulnerability in the Palo Alto Networks PAN-OS web interface enables an authenticated administrator with permission to upload plugins to execute arbitrary code with root user privileges. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.20; PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.11; PAN-OS 10.0 versions earlier than PAN-OS 10.0.7; PAN-OS 10.1 versions earlier than PAN-OS 10.1.2. This issue does not affect Prisma Access.

An improper handling of exceptional conditions vulnerability exists in the Palo Alto Networks PAN-OS dataplane that enables an unauthenticated network-based attacker to send specifically crafted traffic through the firewall that causes the service to crash. Repeated attempts to send this request result in denial of service to all PAN-OS services by restarting the device and putting it into maintenance mode. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.20; PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.9; PAN-OS 10.0 versions earlier than PAN-OS 10.0.5. This issue does not affect Prisma Access.

Certain invalid URL entries contained in an External Dynamic List (EDL) cause the Device Server daemon (devsrvr) to stop responding. This condition causes subsequent commits on the firewall to fail and prevents administrators from performing commits and configuration changes even though the firewall remains otherwise functional. If the firewall then restarts, it results in a denial-of-service (DoS) condition and the firewall stops processing traffic. This issue impacts: PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.9; PAN-OS 10.0 versions earlier than PAN-OS 10.0.5. PAN-OS 8.1 and PAN-OS 10.1 versions are not impacted.

An improper authentication vulnerability exists in Palo Alto Networks PAN-OS software that enables a SAML authenticated attacker to impersonate any other user in the GlobalProtect Portal and GlobalProtect Gateway when they are configured to use SAML authentication. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.19; PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.9; PAN-OS 10.0 versions earlier than PAN-OS 10.0.5. PAN-OS 10.1 versions are not impacted.

An OS command argument injection vulnerability in the Palo Alto Networks PAN-OS web interface enables an authenticated administrator to read any arbitrary file from the file system. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.19; PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.10. PAN-OS 10.0 and later versions are not impacted.

A cryptographically weak pseudo-random number generator (PRNG) is used during authentication to the Palo Alto Networks PAN-OS web interface. This enables an authenticated attacker, with the capability to observe their own authentication secrets over a long duration on the PAN-OS appliance, to impersonate another authenticated web interface administrator's session. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.19; PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.10; PAN-OS 10.0 versions earlier than PAN-OS 10.0.4. PAN-OS 10.1 versions are not impacted.

An information exposure through log file vulnerability exists in Palo Alto Networks PAN-OS software where the connection details for a scheduled configuration export are logged in system logs. Logged information includes the cleartext username, password, and IP address used to export the PAN-OS configuration to the destination server.

An information exposure through log file vulnerability exists in Palo Alto Networks PAN-OS software where secrets in PAN-OS XML API requests are logged in cleartext to the web server logs when the API is used incorrectly. This vulnerability applies only to PAN-OS appliances that are configured to use the PAN-OS XML API and exists only when a client includes a duplicate API parameter in API requests. Logged information includes the cleartext username, password, and API key of the administrator making the PAN-OS XML API request.

An information exposure through log file vulnerability exists in Palo Alto Networks PAN-OS software where configuration secrets for the “http”, “email”, and “snmptrap” v3 log forwarding server profiles can be logged to the logrcvr.log system log. Logged information may include up to 1024 bytes of the configuration including the username and password in an encrypted form and private keys used in any certificate profiles set for log forwarding server profiles. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.18; PAN-OS 9.0 versions earlier than PAN-OS 9.0.12; PAN-OS 9.1 versions earlier than PAN-OS 9.1.4; PAN-OS 10.0 versions earlier than PAN-OS 10.0.1.

Padding bytes in Ethernet packets on PA-200, PA-220, PA-500, PA-800, PA-2000 Series, PA-3000 Series, PA-3200 Series, PA-5200 Series, and PA-7000 Series firewalls are not cleared before the data frame is created. This leaks a small amount of random information from the firewall memory into the Ethernet packets. An attacker on the same Ethernet subnet as the PAN-OS firewall is able to collect potentially sensitive information from these packets. This issue is also known as Etherleak and is detected by security scanners as CVE-2003-0001. This issue impacts: PAN-OS 8.1 version earlier than PAN-OS 8.1.18; PAN-OS 9.0 versions earlier than PAN-OS 9.0.12; PAN-OS 9.1 versions earlier than PAN-OS 9.1.5.

Palo Alto Networks PAN-OS contains a vulnerability in SAML which allows an attacker to bypass authentication.

A format string vulnerability in the Varrcvr daemon of PAN-OS on PA-7000 Series devices with a Log Forwarding Card (LFC) allows remote attackers to crash the daemon creating a denial of service condition or potentially execute code with root privileges. This issue affects Palo Alto Networks PAN-OS 9.0 versions before 9.0.7; PAN-OS 9.1 versions before 9.1.2 on PA-7000 Series devices with an LFC installed and configured. This issue requires WildFire services to be configured and enabled. This issue does not affect PAN-OS 8.1 and earlier releases. This issue does not affect any other PA Series firewalls.

A fundamental design flaw within the RADIUS protocol has been proven to be exploitable, compromising the integrity in the RADIUS Access-Request process. The attack allows a malicious user to modify packets in a way that would be indistinguishable to a RADIUS client or server. To be successful, the attacker must have the ability to inject themselves between the client and server.

A packet processing mechanism in Palo Alto Networks PAN-OS software enables a remote attacker to reboot hardware-based firewalls. Repeated attacks eventually cause the firewall to enter maintenance mode, which requires manual intervention to bring the firewall back online.

This affects the following hardware firewall models: - PA-5400 Series firewalls - PA-7000 Series firewalls

An improper authorization vulnerability in Palo Alto Networks Panorama software enables an authenticated read-only administrator to upload files using the web interface and completely fill one of the disk partitions with those uploaded files, which prevents the ability to log into the web interface or to download PAN-OS, WildFire, and content images.

This issue affects only the web interface of the management plane; the dataplane is unaffected.

An incorrect string comparison vulnerability in Palo Alto Networks PAN-OS software prevents Predefined Decryption Exclusions from functioning as intended. This can cause traffic destined for domains that are not specified in Predefined Decryption Exclusions to be unintentionally excluded from decryption.

A credential disclosure vulnerability in Palo Alto Networks PAN-OS software enables an authenticated read-only administrator to obtain the plaintext credentials of stored external system integrations such as LDAP, SCP, RADIUS, TACACS+, and SNMP from the web interface.

A reflected cross-site scripting (XSS) vulnerability in the GlobalProtect portal feature of Palo Alto Networks PAN-OS software enables execution of malicious JavaScript (in the context of a user’s browser) if a user clicks on a malicious link, allowing phishing attacks that could lead to credential theft.

Web sessions in the management interface in Palo Alto Networks PAN-OS software do not expire in certain situations, making it susceptible to unauthorized access.

A vulnerability in Palo Alto Networks PAN-OS software enables an authenticated administrator to expose the plaintext values of secrets stored in the device configuration and encrypted API keys.

A file disclosure vulnerability in Palo Alto Networks PAN-OS software enables an authenticated read-write administrator with access to the web interface to export local files from the firewall through a race condition.

A cross-site scripting (XSS) vulnerability in Palo Alto Networks PAN-OS software on Panorama appliances enables an authenticated read-write administrator to store a JavaScript payload in the web interface that will execute in the context of another administrator’s browser when viewed.

A vulnerability in the GlobalProtect Gateway in Palo Alto Networks PAN-OS software enables an authenticated attacker to impersonate another user and send network packets to internal assets. However, this vulnerability does not allow the attacker to receive response packets from those internal assets.

A vulnerability in Palo Alto Networks PAN-OS software enables a remote attacker to reboot PAN-OS firewalls when receiving Windows New Technology LAN Manager (NTLM) packets from Windows servers. Repeated attacks eventually cause the firewall to enter maintenance mode, which requires manual intervention to bring the firewall back online.

A reflected cross-site scripting (XSS) vulnerability in the Captive Portal feature of Palo Alto Networks PAN-OS software can allow a JavaScript payload to be executed in the context of an authenticated Captive Portal user’s browser when they click on a specifically crafted link.