CISA: Just-Disclosed Palo Alto Networks Firewall Bug Under Active Exploit

The US Cybersecurity and Infrastructure Security Agency (CISA) is warning that a high-severity security vulnerability in Palo Alto Networks firewalls is being actively exploited in the wild.

The bug (CVE-2022-0028, CVSS severity score of 8.6), exists in the PAN-OS operating system that runs the firewalls, and could allow a remote threat actor to abuse them to deploy distributed denial-of-service (DDoS) attacks against targets of their choice — without having to authenticate.

Two weeks since its disclosure, CISA said that it has now seen the bug being adopted by cyber adversaries in the wild, and it's added it to its Known Exploited Vulnerabilities (KEV) catalogue. Attackers can exploit the flaw to deploy both reflected and amplified versions of DDoS floods.

Exploitation of the issue can help attackers to cover their tracks and location, according to the original Palo Alto Networks advisory issued earlier this month.

"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," according to the firm.

"The good news is that this vulnerability does not provide attackers with access to the victim's internal network," says Phil Neray, vice president of cyber-defense strategy at CardinalOps. "The bad news is that it can halt business-critical operations [at other targets] such as taking orders and handling customer service requests."

He notes that DDoS attacks aren't just mounted by small-time nuisance actors, as is often assumed: "DDoS has been used in the past by adversary groups like APT28 against the World Anti-Doping Agency."

The bug arises thanks to a URL-filtering policy misconfiguration, so instances that use a non-standard configuration are at risk. To be exploited, the firewall configuration "must have a URL filtering profile with one or more blocked categories assigned to a security rule with a source zone that has an external facing network interface," the advisory read.

Exploited in the Wild

Bud Broomhead, CEO at Viakoo, says bugs that can be marshaled into service to support DDoS attacks are in more and more demand by cybercriminals -- and are increasingly exploited.

"The ability to use a Palo Alto Networks firewall to perform reflected and amplified attacks is part of an overall trend to use amplification to create massive DDoS attacks," he says. "Google's recent announcement of an attack which peaked at 46 million requests per second, and other record-breaking DDoS attacks will put more focus on systems that can be exploited to enable that level of amplification."

The speed of weaponization also fits the trend of cyberattackers taking increasingly less time to put newly disclosed vulnerabilities to work — but this also points to an increased interest in lesser-severity bugs on the part of threat actors.

"Too often, our researchers see organizations move to patch the highest-severity vulnerabilities first based on the CVSS," Terry Olaes, director of sales engineering at Skybox Security, wrote in an emailed statement. "Cybercriminals know this is how many companies handle their cybersecurity, so they've learned to take advantage of vulnerabilities seen as less critical to carry out their attacks."

But patch prioritization continues to be a challenge for organizations of all stripes and sizes thanks to the sheer number of patches that are disclosed in a given month — it totals hundreds of vulnerabilities that IT teams need to triage and assess, often without much guidance to go on. And furthermore Skybox Research Lab recently found that new vulnerabilities that went on to be exploited in the wild rose by 24% in 2022.

That said, "any vulnerability that CISA warns you about, if you have in your environment, you need to patch now," Roger Grimes, data-driven defense evangelist at KnowBe4, tells Dark Reading. "The [KEV] lists all the vulnerabilities that were used by any real-world attacker to attack any real-world target. Great service."

He notes that the list is exhaustive: "It isn't just full of Windows or Google Chrome exploits. I think the average computer security person would be surprised about what's on the list. It's full of devices, firmware patches, VPNs, DVRs, and a ton of stuff that isn't traditionally thought of as being highly targeted by hackers."

Time to Patch & Monitor for Compromise

For the newly exploited PAN-OS bug, patches are available in the following versions:

To determine if the damage is already done, "organizations should ensure they have solutions in place capable of quantifying the business impact of cyber-risks into economic impact," Olaes wrote.

He added, "This will also help them identify and prioritize the most critical threats based on the size of financial impact, among other risk analyses such as exposure-based risk scores. They must also enhance the maturity of their vulnerability management programs to ensure they can quickly discover whether or not a vulnerability impacts them and how urgent it is to remediate."

Grimes notes that it's a good idea to subscribe to CISA's KEV emails as well.

"If you subscribe, you'll get at least an email a week, if not more, telling what the latest exploited vulnerabilities are," he says. "It isn't just a Palo Alto Networks problem. Not by any stretch of the imagination."