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CISO PostMortem: Windows Driver 0-Day (CVE-2025-24990) Grants SYSTEM Access, Fuels Ransomware — by CyberDudeBivash

By CyberDudeBivash · 01 Nov 2025 · cyberdudebivash.com · Intel on cyberbivash.blogspot.com

LinkedIn: ThreatWirecryptobivash.code.blog

WINDOWS 0-DAY • LPE • EDR BYPASS • RANSOMWARE

Situation: This is a CISA KEV (Known Exploited Vulnerability) alert. A zero-day flaw, CVE-2025-24990, has been found in the “Agere” universal driver present in *all modern Windows versions*. This is a Local Privilege Escalation (LPE) flaw that allows any user to gain full `NT AUTHORITY\SYSTEM` access. Ransomware gangs are *already* chaining this with phished credentials to bypass EDR and deploy their payloads.

This is a decision-grade CISO postmortem. Your Endpoint Detection and Response (EDR) is configured to *trust* signed Microsoft drivers. This attack, a “Bring Your Own Vulnerable Driver” (BYOVD) variant, exploits that trust. The attacker uses this flaw to *kill your EDR agent* from the kernel (Ring 0) *before* deploying ransomware. Your SOC team is blind. We are providing the kill chain analysis and the mandatory “Hunt & Harden” response plan.

TL;DR — A universal Windows driver flaw (CVE-2025-24990) is being exploited.

• The Flaw: A Local Privilege Escalation (LPE) in a trusted, signed driver.
• The Impact: Instant `SYSTEM` access. This is “God Mode” on a Windows machine.
• The Kill Chain: Phish (Foothold) → Exploit CVE-2025-24990 (Get `SYSTEM`) → Kill EDR Agent → Deploy Ransomware.
• Why EDR Fails: The exploit runs as a *trusted driver* (Ring 0), which has a higher privilege than your *EDR agent* (user-mode or kernel-mode). The EDR is terminated before it can alert.
• THE ACTION: 1) PATCH NOW. This is an emergency, out-of-band patch. 2) HUNT. You *must* assume you are breached. Hunt for the *initial foothold* (phishing) and the exploit’s TTPs. 3) HARDEN. Implement Application Control (WDAC) to block all non-authorized drivers.

Contents

1. Phase 1: The “Ring 0” Exploit (Why a Driver Flaw is a “Game Over” Threat)
2. Phase 2: The Kill Chain (From Phish to SYSTEM to Ransomware)
3. Phase 3: PostMortem – Why Your EDR Was Blind and Helpless
4. The CISO Mandate: A 3-Step “Patch, Hunt, Harden” Plan
5. Tools We Recommend (Partner Links)
6. CyberDudeBivash Services & Apps
7. FAQ

Phase 1: The “Ring 0” Exploit (Why a Driver Flaw is a “Game Over” Threat)

To understand why this is a CISO-level crisis, you must understand the “Protection Rings” of a modern OS.

• Ring 3 (User Mode): This is where your applications live (Chrome, Word, `powershell.exe`). Your EDR agent also lives here.
• Ring 0 (Kernel Mode): This is the *core* of the OS. It’s the “God Mode” space where the Windows Kernel and *drivers* (like the Agere driver) run.

A “normal” LPE exploit tricks a `SYSTEM` process in Ring 3. A driver exploit is infinitely more dangerous. It’s a “Bring Your Own Vulnerable Driver” (BYOVD) attack. The attacker finds a *legitimate, signed* driver (Agere) that has a flaw. They exploit *that* flaw to run their *own* code in *Ring 0*.

Once an attacker has code execution in Ring 0, they *are* the operating system. They are *above* your EDR. They can *unhook* the EDR’s sensors, kill its process, and blind your *entire* security stack. Your EDR cannot stop an attack from a *higher privilege level*. This is a *fundamental bypass* of endpoint security.

Phase 2: The Kill Chain (From Phish to SYSTEM to Ransomware)

This zero-day is not an “initial access” tool. It’s a Local Privilege Escalation (LPE) exploit. Ransomware gangs *love* this. It’s the “key” they use after they’ve already picked the lock.

Stage 1: Initial Access (The Foothold)

The attacker gets onto your server or workstation as a *low-privilege user*. This is almost *always* a simple spear-phishing attack.
An employee receives a “document,” clicks “Enable Macros,” and a fileless malware (PowerShell) foothold is established. The attacker is “in,” but they are just a “user.” They can’t do real damage.

Stage 2: Privilege Escalation (CVE-2025-24990)

The attacker’s script uploads the CVE-2025-24990 exploit. They run it. The exploit targets the vulnerable `agere.sys` driver. In seconds, the memory corruption flaw is triggered, and the exploit spawns a new `cmd.exe` process. This new shell has one difference: its user is `NT AUTHORITY\SYSTEM`.

Stage 3: Defense Evasion (The “EDR Kill”)

This is the *first thing* an attacker does as `SYSTEM`. They *blind* your security.

1. The exploit, now running in Ring 0, *unhooks* your EDR’s API monitoring from the kernel.
2. It runs `sc stop windefend`, `sc stop kaspersky-edr`, `sc stop crowdstrike`.
3. Your SOC dashboard goes “green.” It looks like the endpoint is “healthy,” but in reality, the EDR agent is *dead*.

Stage 4: Deployment (Ransomware)

Now that your EDR is blind and disabled, the attacker *finally* drops the “loud” malware. They download the ransomware payload (e.g., LockBit) and execute it. As `SYSTEM`, it encrypts *everything*. They also use this `SYSTEM` access to move laterally to your Domain Controller. Game over.

Phase 3: PostMortem – Why Your EDR Was Blind and Helpless

This is a CISO postmortem because this attack *will* succeed against 99% of “out-of-the-box” EDR configurations. Your tool failed for two reasons:

1. The “Trusted Driver” Bypass (BYOVD)

Your EDR is configured to *trust* drivers with a valid Microsoft signature. The “Agere” driver *is* a valid, signed driver. The EDR *allows* it to load. The EDR has no way of knowing this “trusted” driver has a “vulnerable” function that the attacker is about to exploit. This is a “Bring Your Own Vulnerable Driver” (BYOVD) attack, and it’s a classic TTP for bypassing EDR.

2. The “Ring 0” Kill

Your EDR agent is just a *program* (Ring 3). The attacker, by exploiting the driver, is running in the *kernel* (Ring 0). This is like a user trying to fight a computer’s operating system. The OS *always* wins. The Ring 0 code can simply *terminate* the Ring 3 EDR process, and there is *nothing* the EDR can do to stop it. It is *fundamentally* out-privileged.

The CISO Mandate: You CANNOT rely on EDR *alone*.
This is why a “detect and block” strategy *fails*. You *must* have a “Hunt & Respond” strategy. You need a 24/7 human MDR team (like ours) that is *not* just looking at EDR alerts. They are *hunting* for the *initial* TTPs (the phish, the *first* anomalous PowerShell) and the “log gaps” (the *second* an EDR agent goes “offline” for no reason).
Explore Our 24/7 MDR Service →

The CISO Mandate: A 3-Step “Patch, Hunt, Harden” Plan

This is an active CISA KEV alert. This is an Incident Response emergency. Drop everything.

Step 1: PATCH NOW (Hours 0-4)

This is your only priority. Microsoft has issued an emergency, out-of-band patch for this.

1. Identify all vulnerable Windows hosts (which is “all” of them).
2. Deploy the emergency patch from Microsoft *immediately* via WSUS or your patch management tool.
3. Reboot. This is a *driver/kernel* level patch. It *requires a reboot*. Do not wait for a “maintenance window.” The maintenance window is *now*.

Step 2: HUNT (Hours 1-24)

You *must assume you are already breached*. Patching locks the door, but the attacker is *already inside*. Your SOC or MDR provider must *immediately* start threat hunting.

• Hunt TTP 1 (The Foothold): Hunt for the *initial access*. Look for new phishing alerts, anomalous logins, or web shells. This is what our PhishRadar AI is built for.
• Hunt TTP 2 (The Exploit): Look for *any* process loading the vulnerable `agere.sys` driver, *especially* if it’s spawned from a “low-privilege” process like `powershell.exe` or `explorer.exe`.
• Hunt TTP 3 (The “Blind Spot”): This is the key. Run a query: “Show me all endpoints where the EDR agent service has *stopped* for *any* reason in the last 7 days.” This is your #1 indicator of a successful `SYSTEM`-level compromise.

This is an active Incident Response (IR) scenario.
If you find *any* of this, you are breached. Call our 24/7 Incident Response hotline. Our digital forensics team will perform memory forensics, find the kernel-level rootkit, and eradicate the attacker.

Step 3: HARDEN (The Long-Term Fix)

You patched this 0-day. The *next* BYOVD attack is coming next week.
The *real* CISO-level fix is Application Control.
Deploy Windows Defender Application Control (WDAC). Create a policy that *only* allows your *known, authorized* drivers to load. This way, even if an attacker gets a foothold, they *cannot* load the “vulnerable” Agere driver to start their exploit. This *proactively* kills the entire kill chain.

Recommended by CyberDudeBivash (Partner Links)

You need a layered defense. Here’s our vetted stack for this specific threat.

Kaspersky EDR
This is your *sensor*. It’s the #1 tool for providing the behavioral telemetry (process chains, memory forensics) that your *human* MDR team needs to hunt.Edureka — Incident Response Training
Train your SecOps team *now* on Windows Internals (Ring 0/Ring 3) and Threat Hunting TTPs.TurboVPN
Secure your admin access. Your RDP/SSH access for *your admins* should be locked down.

Alibaba Cloud (VDI)
A key mitigation. Use Virtual Desktop Infrastructure (VDI). If the VDI is popped, you *burn it* and re-image in seconds. The host is safe.AliExpress (Hardware Keys)
*Mandate* this for all Domain Admins. Get FIDO2/YubiKey-compatible keys. They stop the *post-breach* credential theft.Rewardful
Run a bug bounty program. Pay white-hats to find flaws *before* APTs do.

CyberDudeBivash Services & Apps

We don’t just report on these threats. We hunt them. We are the expert team you call when a zero-day bypasses your EDR.

• Emergency Incident Response (IR): Our 24/7 team will deploy *today* to hunt for the post-exploit TTPs from CVE-2025-24990 and perform kernel-level forensics.
• Managed Detection & Response (MDR): Our 24/7 SOC team becomes your “human sensor,” hunting for the “EDR agent stopped” and “powershell from driver” TTPs.
• Adversary Simulation (Red Team): We will simulate this *exact* BYOVD-to-Ransomware kill chain to test if your EDR and team can *really* detect and stop it.
• PhishRadar AI — Stops the initial spear-phishing email that delivers the Stage 1 foothold.
• SessionShield — Protects your *admin* sessions, so even if the attacker gets `SYSTEM`, we detect their anomalous *session* behavior.

Book 24/7 Incident ResponseBook an Adversary Simulation (Red Team)Subscribe to ThreatWire

FAQ

Q: What is a “Use-After-Free” (UAF) flaw?
A: It’s a memory corruption bug. A program (the driver) uses a piece of memory, “frees” it, but forgets to delete its pointer. An attacker grabs that same piece of memory. When the driver *uses its old pointer*, it accidentally overwrites the attacker’s memory, giving them control.

Q: What is “BYOVD” (Bring Your Own Vulnerable Driver)?
A: It’s an advanced APT TTP. An attacker *intentionally* loads an *old, signed, but vulnerable* driver (like `agere.sys`) onto a *fully patched* machine. They then exploit *that old driver* to get Ring 0 access. This is why Application Control (WDAC) is so critical.

Q: We’re patched. Are we safe?
A: You are safe from *new* attacks using this flaw. You are *not* safe if an attacker *already* breached you. You MUST complete “Step 2: Hunt for Compromise” or call our IR team to do it for you.

Q: How do I hunt for this?
A: You need a behavioral EDR (like Kaspersky) and an expert MDR team. The hunt query is: “Show me anomalous process chains” (e.g., `svchost.exe -> powershell.exe`) and “Show me all EDR agent service-stop events.”

Next Reads

• [Related Post: The 5 “Fileless” Attack TTPs Your EDR is Missing]
• Daily CVEs & Threat Intel — CyberBivash
• CyberDudeBivash Apps & Services Hub

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