A $36 Million Bet on AI-Driven Email Defense

Email security startup AegisAI has secured $36 million in a Series A round led by Battery Ventures, with participation from Accel and Foundation Capital. The announcement came Thursday, bringing the company’s total raised to $49 million since its founding in 2025.

The fresh capital isn’t just a milestone—it’s fuel for a specific mission. AegisAI plans to expand its lineup of autonomous detection agents, push its Vanguard agent toward general availability, and scale its enterprise go-to-market efforts. In plain terms: they’re gearing up for a serious fight against a new breed of cyber threat.

From Google’s Security Team to Email’s Front Lines

AegisAI was founded by Cy Khormaee and Ryan Luo, two veterans of Google’s security team who helped build reCAPTCHA, Safe Browsing, and Web Risk. The company emerged from stealth in September 2025 with a clear thesis: traditional email security is no match for AI-powered attacks.

Their platform is built around a network of AI agents that scrutinize incoming email for phishing, business email compromise, and other threats. Instead of relying on static rules or known-bad signatures, the system evaluates the intent and identity behind each message. It’s a fundamental shift from the blocklist-and-keyword approach that has dominated the industry for decades.

How Vanguard Investigates Threats Like a Human

The product connects to Microsoft 365 and Google Workspace through an API, requiring no changes to a customer’s MX records. That’s a deliberate choice—deployment friction is often the death of security tools, and AegisAI clearly wants to avoid that trap.

In March, the company introduced Vanguard, a companion agent that takes a more proactive approach. It investigates suspicious links and attachments by navigating to them the way a human recipient would, then compiles a threat report within minutes. This mimics the curiosity of a cautious employee—but at machine speed.

The Rise of AI Spear Phishing

AegisAI frames its work around what it calls AI spear phishing: attacks that use language models to research a target, map their professional relationships, and produce a personalized lure at a fraction of the cost such an effort once required. The economics of attack have changed, and so must the defense.

Why Human Training Isn’t Enough

Khormaee, who serves as CEO, didn’t mince words about the threat landscape. “The most immediate, catastrophic risk to your organization isn’t an AI agent hacking your firewall. It’s an AI model manipulating someone in your organization into handing over the keys,” he said.

His critique of traditional security awareness programs is pointed: “If your security program still relies on template-based phishing tests and awareness training, you are training your people to spot last year’s threat, not a capable agent crafting a novel lure just for them.” His conclusion is stark—”When the attack is AI, the defense has to be AI.”

What This Means for the Email Security Market

The funding round signals growing investor confidence in AI-native security solutions. Battery Ventures’ leadership role is notable, given the firm’s history of backing enterprise infrastructure companies. With Accel and Foundation Capital also on board, AegisAI has the backing of three heavyweight investors who clearly see a gap in the market.

The $49 million total funding gives the startup runway to compete with established players in the email security space. But the real test will be whether its AI agents can consistently catch threats that slip past traditional filters—and whether enterprises are ready to trust an AI to guard their inboxes.

For CISOs watching the space, the takeaway is clear: the email security landscape is shifting, and the next generation of tools will look very different from what came before. Whether that’s a good thing depends on how well companies like AegisAI deliver on their promises.

USB Auto-Install: The Unexpected Attack Surface

Plugging in a USB stick feels routine. You expect a quick notification and maybe a driver install. But a team of researchers just turned that mundane process into a full SYSTEM-level compromise on a fully patched Windows 11 machine.

The attack abuses Windows Plug and Play (PnP) to fetch signed vendor software for an emulated USB device. Then it chains privileged installation components to escalate straight to SYSTEM. No zero-day kernel exploits. No password cracking. Just the trust Windows places in signed drivers and its own auto-install logic.

Here’s the scary part: the same PnP path works over Remote Desktop, no physical hardware required — provided Plug and Play or low-level USB redirection is enabled.

How the Windows 11 USB Attack Chain Works

The attack starts with a malicious or emulated USB device that presents itself as legitimate hardware. Windows PnP queries the device, looks for a matching signed driver package, and downloads it from Windows Update or the vendor’s server.

That’s by design. But the researchers found a way to hijack the process mid-stream. Here’s the breakdown:

• Emulated device: The attacker crafts a USB descriptor that mimics a real peripheral, like a network adapter or printer.
• Driver fetch: Windows PnP automatically retrieves a signed vendor driver for the emulated device.
• Privileged component: The driver package includes an installer or utility that runs with elevated privileges.
• SYSTEM escalation: The attacker exploits that privileged execution to drop a payload with SYSTEM rights.

The chain is elegant because it never triggers a UAC prompt. Windows trusts its own PnP pipeline, and the vendor’s signature validates the package as safe.

Remote Desktop USB Redirection Expands the Threat

Physical access was once the limiting factor for USB attacks. The researchers removed that barrier. With Remote Desktop’s Plug and Play redirection or low-level USB redirection enabled, an attacker can trigger the same PnP path remotely.

That means a compromised RDP session — or a malicious admin on the same network — could deliver the emulated USB device virtually. The victim’s Windows 11 machine would fetch the signed driver, run the privileged installer, and hand over SYSTEM access without ever touching a physical port.

Microsoft’s response? The company says the behavior is by design, noting that the attack requires either physical access or an already-compromised RDP session. That’s cold comfort for anyone relying on USB redirection for remote work.

Why Signed Drivers Make This Hard to Stop

Vendor signatures are the crown jewel of Windows driver trust. They tell the OS, “This code is safe to run.” The researchers didn’t break that trust — they weaponized it.

By using a legitimate signed driver’s installer, the attack avoids the usual red flags. Antivirus tools see a valid signature and often skip deep inspection. The result: a stealthy privilege escalation that evades detection.

Mitigations for Windows 11 USB PnP Attacks

There’s no magic patch coming, since Microsoft views this as intended functionality. But you can reduce your exposure:

• Disable USB redirection in Remote Desktop settings unless absolutely necessary.
• Restrict PnP device installation via Group Policy to approved device classes.
• Monitor driver installation events in Event Viewer for unexpected signed driver activity.
• Use device control software to block unauthorized USB devices at the endpoint.
• Limit RDP access to trusted users and networks, and enforce strong authentication.

For most organizations, the biggest win is locking down RDP USB redirection. It’s a feature few users genuinely need, and it’s the easiest remote path to this attack.

What This Means for Windows Security

This research is another reminder that Windows’ convenience features are attack surface. Plug and Play was designed for a world where physical trust was assumed. That assumption no longer holds.

We’ve seen similar issues with Windows driver signature bypass techniques and privilege escalation via legitimate services. The pattern is consistent: attackers abuse what Windows trusts, not what it fails to secure.

For defenders, the takeaway is practical. Audit your RDP configuration. Review driver installation policies. And remember that a signed driver is not a guarantee of safety — it’s just a promise from a vendor who might not know how their installer is being abused.

The researchers’ full technical details remain limited, but the proof-of-concept is clear: Windows 11 USB auto-install is no longer just a convenience. It’s a potential backdoor.

Daxin Rootkit Comes Back From the Dead

A nasty piece of malware that most security teams probably thought was history has just popped up again. Daxin — a kernel-mode rootkit tracked as “srt64.sys” — resurfaced inside a Taiwan manufacturing company, and it brought a friend.

That friend is a previously undocumented backdoor called Stupig. Together, they signal that whoever deployed this toolkit hasn’t retired. They’ve just been waiting.

Daxin first came to light in March 2022, when Symantec (now owned by Broadcom) published a detailed write-up. At the time, the evidence pointed to targeted attacks aimed at specific organizations. The malware was linked to a China-based threat actor, though attribution in cyberspace always comes with caveats.

Now, more than four years later, the same rootkit shows up again. That’s a long gap. Most malware families fade away or get replaced by newer tooling. Daxin apparently didn’t get the memo.

What Exactly Is Daxin?

Daxin is not your run-of-the-mill remote access trojan. It operates at the kernel level, which means it runs with the highest privileges on a Windows system. That gives attackers the ability to hide processes, manipulate system calls, and essentially become invisible to standard security software.

Symantec’s original research described it as a sophisticated, modular framework. It wasn’t just a backdoor — it was a full toolkit for stealthy espionage. The fact that it’s resurfaced in a manufacturing environment fits a broader pattern of attackers targeting industrial and critical infrastructure sectors.

Why Taiwan Manufacturing?

Taiwan’s manufacturing sector is a prime target for state-sponsored espionage. The island is home to a dense supply chain for semiconductors, electronics, and precision machinery. A foothold in one firm can potentially ripple through the entire ecosystem.

In this case, the victim was a manufacturing company, though the report doesn’t name it. That’s typical — most victims prefer to stay anonymous and quietly clean up their networks.

Meet Stupig: The New Backdoor on the Block

Alongside the Daxin rootkit, researchers found a previously unknown backdoor they’ve named Stupig. That’s an odd name, but it’s memorable. The backdoor appears to be a companion piece to Daxin, likely used for post-exploitation activities.

While Daxin handles the stealthy kernel-level persistence, Stupig probably serves as a more conventional backdoor — giving attackers remote access, file transfer capabilities, and command execution. The combination is dangerous: one component hides, the other acts.

Researchers haven’t yet published a full technical breakdown of Stupig’s capabilities. But the fact that it’s been deployed alongside a known state-sponsored rootkit suggests it’s not amateur hour.

What This Means for Defenders

If you’re running a security team at a manufacturing firm, this news should hit close to home. The threat actor behind Daxin is patient. Four years between deployments is a long time to wait, but they clearly haven’t moved on.

Here are some practical takeaways:

• Kernel-level detection matters. If your EDR doesn’t monitor kernel drivers, you’ll miss Daxin entirely.
• Check for signed but malicious drivers. Daxin uses a driver file (srt64.sys). Legitimate-looking drivers are a common evasion technique.
• Hunt for dual-component infections. If you find one backdoor, look for others. Attackers often deploy multiple tools.
• Monitor outbound traffic. Backdoors need to phone home. Unusual C2 connections are often the first sign of trouble.

For more on how attackers hide their tracks, you might want to read about kernel-level malware detection techniques or check out our guide on identifying backdoor indicators of compromise.

The Bigger Picture: State-Sponsored Espionage Isn’t Going Away

The reappearance of Daxin is a reminder that cyber espionage campaigns don’t follow a timeline. Threat actors re-use tools when they work. They don’t care if the malware is “old” — they care if it’s effective.

Symantec’s 2022 report linked Daxin to a China-nexus actor, and nothing in this latest sighting contradicts that assessment. But attribution is always tricky. The tools are what we can see; the operators behind them remain in the shadows.

For now, the key takeaway is simple: Daxin is back, it’s paired with a new backdoor, and it’s targeting manufacturing. If you’re in that sector, treat this as a wake-up call.

Security teams should also review their incident response playbooks for rootkit infections before they need them. Preparation is cheaper than cleanup.

This story is still developing. Researchers will likely publish more technical details about Stupig in the coming weeks. For now, the message is clear — the threat landscape doesn’t stand still, and neither should your defenses.