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Police in Spain have arrested a 16-year-old whom investigators suspect of running the KillSec ransomware group. KillSec is accused of stealing data from organizations and threatening to publish it on its leak site unless they paid. The 16-year-old was one of 3 people arrested on September 30, when police also took control of that site. Investigators identified him as KillSec's suspected administrator and main operator,  Hamburg police said  on October 1. Police and prosecutors in Hamburg, Germany, led the operation. The Guardia Civil and the Mossos d'Esquadra, both Spanish police forces, detained him in Alicante and searched a home and an office at a hotel in the province. Their joint statement,  carried by elperiodic.com , calls him one of the group's administrators and its presumed main administrator. The other 2 people arrested are in their 20s, one in the U.K. and one in Romania, a spokesperson for Europol, the European Union's police agency,  told Reute...

This week, the useful words are boring ones: inspect, cache, compile, store, trust. Each sounds harmless. Each can become an attack path when a system does a little more than people expect. A model check can run code. A cache can mix up requests. A public secret can stay useful for years. That is the lesson running through the list. Attackers do not always need a brilliant new trick. They can hide commands in public infrastructure, reuse old flaws, abuse weak defaults, or let automation stitch together a rough path that still works. Faster tools are changing the pace, but basic mistakes are still doing plenty of the work. So the interesting question this week is not “what broke?” It is “what did we assume was safe because it looked ordinary?” The full list has answers. The threats change every week. Subscribe, and we’ll alert you when each new ThreatsDay Bulletin is out.

Cybersecurity researchers have shed light on a WordPress compromise in which threat actors deployed multiple persistence mechanisms to ensure that the final payload kept returning without having to infect the site again. The backdoor has been codenamed SC after the "SC_" markers present in the injected content. Sucuri has described the malware as a "self-healing mesh" that's blockchain-controlled. "The payload lives in at least eight places at once, spread across files, the database, and shared memory, and every one of those places can rebuild all the others," security researcher Gabriel Barbosa said . "Delete the plugin and a drop-in rewrites it. Delete the drop-in and the theme rewrites it. Clean every file on disk, and the next page load restores the whole set from the database or from a shared-memory segment. The result is a circular system with no single point you can remove to stop it." According to Sucuri, the malware does no...

Every security leader at a bank, insurer, or asset manager has had a version of this conversation: Security wants to eliminate a class of vulnerabilities. Engineering explains what it would take to upgrade the platform where they live. Somebody prices out the regression testing. Somebody else raises the change-freeze calendar. The finding gets an exception, a compensating control, and a date eighteen months out on the roadmap to address it. Nobody in that conversation is being unreasonable. Financial services carry more legacy software than almost any other industry for a few reasons: decades of accumulated infrastructure, regulatory obligations that reward stability, and applications where an hour of downtime is unacceptable. In that environment, minimizing change is risk management. Every dependency bump, every base image swap, every migration is a chance to break something that clears trades or moves money. So the instinct to stick to the status quo has been sound. The problem...

OpenAI on Wednesday said it identified and disrupted a coordinated distillation campaign that was designed to illicitly extract protected reasoning from its artificial intelligence (AI) models. A "core cluster of the activity," going back to the first week of July, has been attributed to individuals associated with Moonshot AI, a Chinese AI company based in Beijing. It did not cite any technical evidence to back this assessment, likely owing to security reasons. "The operators did not break our encryption, compromise a database, or gain direct access to stored user conversations," OpenAI said . "Instead, they manipulated model interactions so that protected reasoning could be reproduced in forms visible to the requester in a coordinated, scaled manner that violated our terms of service." The activity is said to have begun on July 1, 2026, initially at a low volume before it spiked on July 24 and 25, 2026, to 16,000 attempted requests using a relevan...

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) on Wednesday added a critical authentication bypass flaw impacting Cisco Catalyst SD-WAN Manager to its Known Exploited Vulnerabilities ( KEV ), following reports of active exploitation. The vulnerability, tracked as CVE-2026-76504 (CVSS score: 9.8), could allow an unauthenticated, remote attacker to access an affected system with the privileges of the admin user. "Cisco Catalyst SD-WAN Manager contains a hex encoding vulnerability that could allow an unauthenticated, remote attacker to access an affected system with privileges of the admin user due to improper handling of URI encoding in an HTTP request," CISA said. Successful exploitation could allow an attacker to sidestep authentication by sending a crafted HTTP request to the API of the affected system, and gain access to the API as the admin user.

Google on Wednesday announced its latest frontier artificial intelligence (AI) model, Gemini 4 Argon , that it said is being rolled out to a set of trusted cyber defenders through its Fairwind Program. "It delivers frontier performance in complex workflows across real-world software engineering, enterprise knowledge work like legal and finance, and cybersecurity defense," Koray Kavukcuoglu, senior vice president of Google DeepMind and Chief AI Architect at Google, said . The development comes nearly a month after the tech giant unveiled Gemini 3.8 Flash Cyber , which it described as the most capable cybersecurity model. Like similar models from rivals Anthropic and OpenAI, Argon is assessed to be highly capable at autonomously finding, validating, and patching critical software vulnerabilities. This includes a previously unknown critical vulnerability exposing sensitive personal information across healthcare software used by hospitals worldwide. Google did not reveal...

Security researchers have published the first public proof-of-concept for CVE-2026-86950 , an Apple CoreGraphics flaw Apple says may have been used in attacks against specific targeted individuals. The trigger is a malicious PDF with a crafted embedded font that crashes unpatched iPhones and Macs. The code causes a crash, not an execution error. Turning the memory corruption into a working exploit is separate work the analysis does not demonstrate. Apple patched the flaw on  September 28 , crediting Meta Product Security with the discovery and noting it may have been used in an "extremely sophisticated attack against specific targeted individuals on versions of iOS before iOS 27." The U.S. Cybersecurity and Infrastructure Security Agency  added the flaw  to its Known Exploited Vulnerabilities catalog the following day, requiring federal agencies to apply the fix by October 2. Apple has not listed iOS 27 or macOS Golden Gate 27 as affected in the September 28 advi...

Cryptocurrency exchange Bitget on Wednesday confirmed that attackers who stole $387.5 million last week exploited a zero-day flaw in third-party security products, citing ongoing investigation findings from SlowMist. "Their investigation identified malicious activity involving third-party security products, including a zero-day vulnerability, and recovered a customized tool used by the attacker to initiate unauthorized withdrawals," Bitget said in a post on X. On September 24, 2026, the cryptocurrency exchange disclosed that threat actors stole $387.5 million from its hot and warm wallets through a series of unauthorized transfers, prompting it to halt all withdrawals temporarily. Close to $1.1 million in cryptocurrency assets have been frozen by Circle, Tether, and NEAR Intents. In a subsequent analysis , Bitget said the attackers exploited the flaw to obtain high-level internal credentials and use them to issue fraudulent withdrawal commands to the wallet system ...

MetaMask on Thursday said it's responding to what it described as an "ongoing security incident" impacting part of its infrastructure. "We are actively addressing and remediating the issue internally, in coordination with external partners and security advisors," the software cryptocurrency wallet maker said . "At this time, we have identified no immediate threat to MetaMask wallets." MetaMask did not disclose any additional details related to the security issue.  As a precautionary measure, MetaMask said it's proactively exiting affected validators within its non-custodial staking operations, in coordination with clients and partners. "As a reminder, our staking operations are non-custodial in nature, and we do not manage withdrawal keys for stake on behalf of our clients," it added. Lido, a decentralized liquid staking solution for Ethereum, said MetaMask has taken steps to protect client assets related to its operated Ethereum...

Threat actors have been observed exploiting a critical pre-authentication command injection vulnerability in Citrix NetScaler ADC and NetScaler Gateway to drop web shells and attempt theft of configuration data. LevelBlue's Threat Hunt Operations & Research (THOR) team, which analyzed the exploitation activity across multiple customer environments, said it identified malicious NetScaler authentication events containing attacker-controlled usernames designed to weaponize CVE-2026-88771. CVE-2026-88771 (CVSS score: 9.5) is an improper input validation vulnerability that could allow an unauthenticated attacker to execute arbitrary commands.  The security flaw, along with CVE-2026-88772, was disclosed last week after reports that the Dutch National Cyber Security Centre (NCSC-NL) reportedly sent a pre-notification to organizations in the Netherlands that urged organizations to shut their appliances down, citing active exploitation. As of writing, there are currently no d...

Threat actors have weaponized a now-patched security flaw in Zimbra Collaboration Suite (ZCS) to deploy web shells and access mailbox data, according to findings from the Microsoft Security Research team. The attack exploits CVE-2026-73570 (CVSS score: 8.9), an unauthenticated operating system command injection flaw that can lead to remote code execution when Simple Network Management Protocol (SNMP) notifications are enabled and the optional zimbra-snmp package is installed. Exploitation of CVE-2026-73570 can be triggered by a specially crafted SMTP request (i.e., email) against exposed Zimbra servers without requiring authentication or user interaction. The vulnerability was patched by Zimbra in July 2026 with the release of version 10.1.20. "Following successful exploitation, observed activity included deployment of JSP web shells and reverse shells, privilege escalation, persistent remote-access tooling, and memory-backed execution," the tech giant said . "Th...

Microsoft has warned of phishing campaigns distributing an installer for the MSP360 Remote Monitoring and Management (RMM) software under the guise of meeting invitations, PDF-themed lures, software update prompts, and other social-engineering content. "Once executed, the legitimate MSP360 installer, distributed under a deceptive file name established remote management access on affected devices and enabled threat actors to gain an initial foothold using trusted administrative software," the Microsoft Security Research team said . The initial foothold is then used to download and install a ConnectWise ScreenConnect client, offering threat actors a redundant remote-access channel to compromised endpoints. The access is then abused to deliver additional tools and carry out information collection and credential-access operations. The activity has not been attributed to any known threat actor or group. The multi-stage intrusion chain, which the Windows maker detected in Ju...

Attackers are exploiting a new critical zero-day flaw in Cisco Catalyst SD-WAN Manager, the system companies use to manage their Cisco SD-WAN networks, Cisco said in an  advisory  on September 30. The flaw, CVE-2026-76504 , could allow a remote attacker with no login access to use the Manager's API as the admin user. Fixed releases are available, and there is no workaround. It carries a CVSS score of 9.8 out of 10. It sits in the part of the Manager's API that handles login sessions. The Manager mishandles URI encoding in an HTTP request. A crafted request can therefore bypass an authentication rule intended to restrict access to a single API endpoint. The attacker needs no credentials, only the ability to send that request to the Manager's API. Managers exposed to the internet are at risk of compromise, according to Cisco. By default, the admin user holds the netadmin role, which is allowed to perform all operations on the device. Cisco said its Product Security I...

Threat actors are abusing ChatGPT Custom GPTs to disguise them as legitimate product offerings and direct unsuspecting victims to malicious sites that employ ClickFix lures to deliver malware. Huntress, which observed the activity in late September 2026, said it marks the abuse of yet another feature in trusted artificial intelligence (AI) platforms. Prior campaigns have weaponized shared conversations with AI chatbots and malicious Claude Artifacts to distribute stealer malware and remote access trojans (RATs). Custom GPTs refer to a personalized version of ChatGPT that, as the name implies, allows users to define custom instructions, upload reference files, and enable specific skills to handle unique tasks without any coding. They are hosted on the legitimate ChatGPT website with the Custom GPT name at the top. "In the incidents we saw, victims interacted with an attacker-created Custom GPT, which was programmed to respond to their prompts with a message that includ...

Given that the browser is where business apps are accessed and used, it makes sense that attacks are happening there too. Most breaches today begin in a browser session. Often, they never leave it, with the entire attack chain from initial access to exfiltration playing out in the browser. Here are the six most dangerous techniques that should be on every security team's radar in 2026. 1. Phishing for credentials and sessions Modern phishing kits don't just steal passwords — they intercept live sessions. Reverse-proxy adversary-in-the-middle (AiTM) kits like Tycoon2FA, Sneaky2FA, and Evilginx relay credentials and session tokens in real time, bypassing most forms of MFA. These kits are sold as turnkey Phishing-as-a-Service platforms with anti-bot protection, dynamic lure generation, and automated session replay — reducing the barrier to sophisticated phishing to effectively zero. At the same time, phishing delivery has moved well beyond email — attackers deliver link...