Researchers and threat hunters are scrambling to respond to an actively exploited authentication-bypass vulnerability affecting Palo Alto Networks customers’ firewalls. 

The company initially tagged CVE-2026-0257 with a medium-severity rating when it disclosed the defect May 13, but quickly reassessed it as critical after Rapid7 observed and confirmed active exploitation in the wild. The Cybersecurity and Infrastructure Security Agency followed suit, and added the vulnerability to its known exploited vulnerabilities catalog Friday.

The escalated threat posed by the defect, which allows remote attackers to bypass security restrictions and establish a VPN connection to an affected firewall, showcases how quickly a seemingly mild vulnerability can turn into an urgent warning. 

“Palo Alto Networks is actively monitoring limited exploitation attempts targeting CVE-2026-0257 on unpatched PAN-OS devices where mitigations have not been applied,” a company spokesperson said in a statement. The company on Friday urged all customers to immediately apply the patch or follow its recommended steps for mitigation. 

The vendor and Rapid7, which first observed exploitation May 17 in a customer environment, declined to say how many organizations are impacted thus far. Yet, Douglas McKee, director of vulnerability intelligence at Rapid7, warned: “We’ve continued to see new victims roll in, including a couple of customers hit within just an hour of each other during a second wave of activity” on May 21. 

Jake Knott, security researcher at watchTowr, told CyberScoop the vulnerability and resulting exploits follows a recurring trend wherein attackers target exposed network edge devices and rapidly identify, develop and weaponize exploits for initial access. 

“This is yet another authentication bypass on a device whose sole job is to guard the front door to an organization’s network,” he said. “What stands out is how simple it is — an attacker can forge a valid authentication cookie using nothing more than the appliance’s publicly available TLS certificate. The entire exploit is a single HTTP request.”

The vulnerability has a few requisites that limit exposure, specifically posing risk to some Palo Alto Networks customers running GlobalProtect portal or gateway configured to enable authentication override cookies. 

“The cookie encryption and decryption certificate must be reused with another feature, which potentially exposes the public key for that certificate,” said Caitlin Condon, vice president of security research at VulnCheck.

“It’s difficult to say how many deployments meet those criteria for exploitability, but Palo Alto Networks firewalls have a very large footprint, which means even uncommon configurations can present significant attack surface area,” she added.

Rapid7 said the same attacker or group is likely responsible for both waves of exploitation last month, but in many cases attackers are not establishing a full VPN connection or moving to other parts of the impacted network. 

The attackers are “highly opportunistic and clearly monitor the security research community,” McKee said. “Attackers are purposefully weaponizing medium-severity vulnerabilities, which are typically lower priority or blind spots for organizations.”

Multiple threat clusters are swarming to the opportunity and quickly adapting to published research.  Researchers have not attributed the malicious activity to any specific threat groups. 

“Their exact origins and long-term objectives remain unclear, as they currently seem focused purely on opportunistic initial access rather than targeted, long-term espionage,” McKee said. 

Palo Alto Networks said it discovered the vulnerability internally through its use of frontier AI tools. Yet, within days of its public disclosure, initial assessments were proven inadequate.

“This is a pattern we continue to see — the urgency only arrives after exploitation is underway,” Knott said. “Organizations that wait for confirmation of active exploitation before patching will consistently find themselves reacting too late.”

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Attackers returned once again to a common target with a massive user base by exploiting a max-severity zero-day vulnerability affecting Cisco Catalyst SD-WAN Controller and Manager.

The threat group behind the “limited” number of attacks Cisco is aware of thus far are also linked to a series of previously disclosed vulnerabilities in the vendor’s firewalls and SD-WAN systems, the company said in a threat advisory Thursday.

The authentication bypass vulnerability — CVE-2026-20182 — has a CVSS rating of 10 and “behaves like a master key,” Douglas McKee, director of vulnerability intelligence at Rapid7, wrote in a blog post. 

“An attacker can present themselves to the controller as a trusted network router and, if the system accepts that claim without properly validating it, they can obtain the highest level of administrative access,” he added. “That is the cybersecurity version of a Jedi mind trick.”

Rapid7 discovered and reported the vulnerability to Cisco on March 9, and Cisco said it became aware of limited exploitation of the vulnerability earlier this month. The vendor disclosed and released a patch for the vulnerability Thursday, and the Cybersecurity and Infrastructure Security Agency quickly added the defect to its known exploited vulnerabilities catalog.

Cisco did not explain what occurred during that two-month window. Yet, the disclosure and warning from researchers marks another challenge for Cisco customers that have confronted a flood of actively exploited vulnerabilities affecting the vendor’s network edge software since late February. 

Cisco isn’t the only security vendor facing an onslaught of attacks on its customers, but it is among the most heavily targeted. CISA has added seven vulnerabilities affecting Cisco SD-WANs and firewalls to its known exploited vulnerabilities catalog in less than three months.

Cisco Talos researchers attributed the latest round of zero-day attacks to UAT-8616, the same attackers that exploited a pair of separate zero-days in Cisco’s network edge software for at least three years before the activity was discovered and reported in February. 

The company, which described the exploitation of the new zero-day as ongoing, once again declined to answer questions about the origins or motivations of UAT-8616. 

“We strongly recommend customers apply the available fixed software releases and follow the guidance provided in the advisories and Cisco Talos blog,” a spokesperson for the company said in a statement.

Cisco Talos researchers also warned that UAT-8616 and at least 10 other threat groups have chained together and achieved “widespread in-the-wild active exploitation of three vulnerabilities in unpatched Cisco Catalyst SD-WAN Infrastructure.” The company previously disclosed and released patches for the vulnerabilities — including CVE-2026-20122, CVE-2026-20128 and CVE-2026-20133 — in February. 

Rapid7 said it discovered the latest critical authentication bypass vulnerability when it was researching CVE-2026-20127, a previous zero-day the Five Eyes identified and confirmed as actively exploited by UAT-8616 in late 2025. Authorities and Cisco waited at least two months to disclose and patch the vulnerability, and share emergency mitigation guidance.

That campaign, which got underway at least three years prior, marked the second series of actively exploited zero-days in Cisco edge technology in less than a year. Both campaigns prompted CISA to issue emergency directives months after the attacks were first detected, and both attack sprees were underway for at least a year before they were discovered. 

The latest zero-day, which bypasses authentication in the same control-plane service as CVE-2026-20127,  requires no credentials or prior knowledge of the target environment for exploitation, Jonah Burgess, senior security researcher at Rapid7, told CyberScoop.

“Cisco confirmed it affects all deployment types, including on-premises, cloud, and FedRAMP environments. The SD-WAN Controller manages routing and policy for the entire overlay network, so a single compromised controller can potentially give an attacker influence over every branch, data center, and cloud edge connected to that fabric,” Burgess added.

His colleague at Rapid7, McKee, said attackers have become very good at turning weaknesses in central network infrastructure into high-impact operations. 

“Compromising one branch router is useful. Compromising the controller that manages the entire estate is a very different conversation. Now you are talking about the ability to reroute traffic, intercept communications, push malicious configuration, or simply break connectivity across the whole organization,” he wrote.

“That is the real paradox here,” McKee added. “The same architecture that gives defenders scale and simplicity can also give attackers a single point of catastrophic leverage.”

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Attackers are actively exploiting a Linux vulnerability in the wild, and researchers warn that the fallout could be broad — anyone with authenticated local access can leverage it to gain total control of a system. 

But the story behind CVE-2026-31431 is almost as interesting as the bug itself. Theori, the company that discovered the bug, leaned heavily on AI to find and initially disclose it. The result is a case study that  underscores the challenges that occur when the relentless hunt for defects collides with marketing impulses and inflated AI-generated language that was long on bluster but lacked technical details. 

Theori dubbed the high-severity vulnerability “Copy Fail” with a vanity domain containing AI-generated content, and warned that every mainstream Linux kernel built since 2017 is in scope of potential exploitation resulting in root access. 

Theori’s AI-powered penetration testing platform, Xint, discovered the local privilege-escalation flaw in a Linux kernel module and reported it to the Linux kernel security team March 23. Major Linux distributions affected by the vulnerability had issued patches prior to Theori’s disclosure, which it published alongside a proof-of-concept exploit. 

The Cybersecurity and Infrastructure Security Agency added CVE-2026-31431 to its known exploited vulnerabilities catalog Friday.

Researchers have yet to determine how many organizations have been impacted by the flaw, but they noted that critical requirements for exploitation, specifically local access achieved through a separate exploit or pathway to unauthorized access, should limit potential exposure.

“The attacker would need to have already established a foothold on the target system either through some means of legitimate access or another exploit,” Spencer McIntyre, secure researcher at Rapid7, told CyberScoop. “That’s a large limiting factor since this vulnerability would therefore need to be paired with another.”

Theori’s disclosure turned heads among other vulnerability researchers who noted the defect’s broad potential impact, but also for lacking details about the proof-of-concept exploit. 

“The exploit is real, there is something to worry about, but understandably, teams now have to do additional validation to know how to parse the extreme AI FUD (fear, uncertainty and doubt) from [Theori’s] blog post,” Caitlin Condon, vice president of security research at VulnCheck, told CyberScoop. 

“It’s not helpful that the blog is AI slop, because it detracts from technical reality,” she added. 

Theori acknowledges it used AI to discover and describe the vulnerability, explaining that it’s focusing on finding and fixing a large amount of defects. 

“We used AI to help craft the disclosure site and the blog post to help speed things up, but all material was thoroughly reviewed by our internal teams for accuracy,” said Tim Becker, senior security researcher at Theori. 

Theori is intentionally withholding additional details until the patch is broadly applied, he added.

“We stand by our technical description of the vulnerability. Helping downstream users to understand the impact of a security bug has always been a challenge for security researchers,” Becker said. “Copy Fail allows for trivial privilege escalation on most desktop and server Linux distributions. It also has implications for containerization including Kubernetes.”

Other researchers have drawn similar conclusions, noting that exploitation can be automated and doesn’t require specialization. 

Meanwhile, hundreds of additional proof-of-concept exploits have surfaced since the vulnerability was disclosed five days ago. “As expected, the majority of these appear to be copycat AI PoCs that do nothing but add banners or different colors to the command-line interface. Many new PoCs are simply ports of the original AI PoC to a different programming language,” Condon said. 

“Organizations should exercise caution when running untested research artifacts, including AI-generated exploit code that isn’t fully explained,” she added. 

Becker said Theori is aware of the burden defenders confront, and insists the company’s reports contain enough information for organizations to quickly triage and validate its findings.

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A severe authentication bypass vulnerability in cPanel, one of the most widely deployed web hosting control panel platforms on the internet, is being actively exploited in the wild, according to security researchers and hosting providers.

The vulnerability, tracked as CVE-2026-41940, affects all supported versions of cPanel and WebHost Manager (WHM) released after version 11.40, as well as WP Squared, a WordPress hosting management panel built on the cPanel platform. Internet scans conducted by security firm Rapid7 using the Shodan search engine identified approximately 1.5 million cPanel instances exposed online, though the precise number of vulnerable systems remains unknown.

cPanel released a patch Tuesday. By that point, exploitation had already been underway. KnownHost, a hosting provider that relies on cPanel, said earlier this week that successful exploits had been observed in the wild prior to any fix being made available. 

The Cybersecurity and Infrastructure Security Agency added the CVE to its Known Exploited Vulnerabilities (KEV) list Thursday. 

Cybersecurity firm watchTowr provided technical details in a blog posted Wednesday: The flaw stems from improper handling of user input during the login process. When a user attempts to log in, cPanel writes data from the request into a server-side session file before verifying the user’s identity. An attacker can exploit this by embedding hidden line breaks into the password field of a login request — characters cPanel fails to strip out — allowing arbitrary data to be injected directly into that file.

Through a secondary step, also involving a deliberately malformed request, the injected data gets promoted into the session’s active cache, where cPanel reads it as legitimate. Once that happens, the system sees the session as already authenticated and skips password verification entirely, granting access without ever checking the user’s actual credentials.

cPanel has published a detection script designed to scan session files for indicators of compromise, including sessions that contain injected authentication timestamps, pre-authentication sessions with authenticated attributes, and password fields containing embedded newlines. WatchTowr separately released a “Detection Artifact Generator” that administrators can use to verify whether their instances remain vulnerable.

Namecheap, a major domain registrar and hosting provider, took the step of temporarily blocking connections to cPanel and WHM ports 2083 and 2087 ahead of patch availability, citing the need to protect customers while an official fix was pending. The company began applying the patch after cPanel’s release earlier this week.

cPanel’s patched releases address the issue across seven version branches, from 11.110.0 through 11.136.0, as well as WP Squared version 11.136.1. The company’s advisory notes that the fix ensures potentially dangerous input is scrubbed automatically within the core session-saving process, rather than depending on each individual part of the codebase to do so separately. The patch also adds handling for cases where a per-session encryption key is missing, a condition the original code failed to account for and that attackers were able to exploit to bypass password encoding entirely.

The CVE has been given a 9.8 on the CVSS scale. 

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Cisco customers have confronted a flood of actively exploited vulnerabilities affecting the vendor’s network edge software since late February, and researchers say that five of the nine vulnerabilities Cisco disclosed in its firewalls and SD-WAN systems over the past three weeks have already been exploited in the wild. 

Attackers exploited a pair of these defects — zero-day vulnerabilities in Cisco SD-WANs — for at least three years before the vendor and authorities discovered and issued warnings about the threat. Cisco disclosed an additional five SD-WAN vulnerabilities that same day, and three of those defects have since been confirmed actively exploited as well.

Weaknesses lurking in Cisco security products don’t end there. Amazon Threat Intelligence on Wednesday said one of the two max-severity defects Cisco reported in its firewall management software earlier this month has been actively exploited by Interlock ransomware since Jan. 26, more than a month before those vulnerabilities were publicly disclosed.

Some organizations, officials and members of the security community at large have missed widening risks as more of the defects come under attack. The flurry of Cisco SD-WAN and firewall vulnerabilities includes defects with low CVSS ratings, zero-days and others that were determined actively exploited after disclosure.

“These are not random bugs in low-value software. These are management-plane and control-plane weaknesses in devices at the network edge, which often function as trust anchors in enterprise environments,” Douglas McKee, director of vulnerability intelligence at Rapid7, told CyberScoop.

“If you compromise SD-WAN or firewall management, you’re landing on policy, visibility, routing, segmentation, and, in many cases, administrative trust over a large swath of the environment,” he added. “Attackers know that and, when they find a pre-auth path into those systems, especially one that can be chained to root, that’s about as attractive as it gets.”

The full slate of recently disclosed Cisco vulnerabilities affecting these systems include:

• SD-WAN vulnerabilities: CVE-2026-20127, CVE-2022-20775, CVE-2026-20122, CVE-2026-20126, CVE-2026-20128, CVE-2026-20129 and CVE-2026-20133
• Cisco Secure Firewall Management Center software vulnerabilities: CVE-2026-20079 and CVE-2026-20131

Researchers from multiple firms and Cisco have observed or been notified of active exploitation of CVE-2026-20127, CVE-2022-20775, CVE-2026-20122, CVE-2026-20128 and CVE-2026-20131.

The Cybersecurity and Infrastructure Security Agency has only added two of the defects — CVE-2022-20775 and CVE-2026-20127 — to its known exploited vulnerabilities catalog thus far. The agency, which last week added new hunting and reporting requirements to an emergency directive it issued for the defects in late February, did not answer questions about the updated order or explain why other actively exploited Cisco vulnerabilities haven’t been added to the catalog. The agency has been operating under a funding shutdown since February.

Interlock ransomware hits Cisco firewalls

The ongoing ransomware campaign Amazon Threat Intelligence spotted involving CVE-2026-20131 confirmed “Interlock had a zero-day in their hands, giving them a week’s head start to compromise organizations before defenders even knew to look,” researchers said Wednesday.

Interlock’s observed attack path and operations are extensive, including post-compromise reconnaissance scripts, custom remote access trojans, a webshell and legitimate tool abuse. Amazon did not identify specific victims, and said the group threatens organizations with data encryption, regulatory fines and compliance valuations.

“Interlock has historically targeted specific sectors where operational disruption creates maximum pressure for payment,” Amazon Threat Intelligence researchers said in the blog post. These sectors include education, engineering, architecture, construction, manufacturing, industrial, health care and government entities. 

4 Cisco SD-WAN defects under attack

The swarm of vulnerabilities in Cisco SD-WANs poses additional risk for customers. Cisco Talos previously attributed long-running attacks involving CVE-2026-20127 and CVE-2022-20775 to UAT-8616, but it’s unclear if the same threat group is responsible for all of the Cisco SD-WAN exploits. 

“Other threat groups are likely to pick up public research in order to weaponize or adapt it opportunistically, so we may see follow-on attempts by additional threat actors, including low-skilled attackers,” Caitlin Condon, vice president of security research at VulnCheck, told CyberScoop.

Researchers said vulnerabilities are often disclosed in clusters after a meaningful defect is identified in a specific product, such as Cisco’s SD-WAN systems.

Cisco declined to answer questions and said customers can find the latest information on its security advisories page.

Condon and McKee both noted that Cisco has been responsive in releasing software fixes, threat-hunting intelligence and, in the case of the SD-WAN zero-days, coordinated government guidance. 

“This is what a good crisis response is supposed to look like once exploitation is identified,” McKee said. 

“The harder question is whether the industry is getting early-enough visibility into the defects in edge-management software that sophisticated actors are clearly prioritizing,” he added. “Are our organizations equipped with the right people and tools to perform this level of exposure management?”

The expanding exploits Cisco customers are combating on firewalls and SD-WANs is a reminder that organizations shouldn’t deprioritize less notorious vulnerabilities or those with lower CVSS scores, Condon said. 

“Several of the exploited vulnerabilities in this tranche of Cisco SD-WAN bugs don’t have critical CVSS scores, meaning teams using CVSS as a prioritization mechanism might miss medium- or high-scored flaws that still have real-world adversary utility,” she added.

The attacks also collectively reflect a persistent pattern of attackers targeting network edge systems from multiple vendors, including Cisco.

“Attackers continue to treat network edge and management infrastructure as prime real estate, and when defenders see pre-authentication, management-plane flaws with evidence of pre-disclosure exploitation, they need to assume compromise, not just exposure,” McKee said. 

“Attackers are investing time and capability into finding and operationalizing previously unknown defects in Cisco edge and management infrastructure because the payoff is enormous,” he added. “These platforms give you a privileged position, broad visibility, and a path to durable access inside high-value organizations. That’s exactly why they keep getting hit.”

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