CISA Alert: Critical Cisco ISE Vulnerabilities Under Active Attack—Here’s What Enterprises Must Know and Do Now

Imagine waking up to find your organization’s network exposed, with attackers already probing for a way in. This isn’t a distant threat—it’s happening right now. On July 28, the U.S. Cybersecurity and Infrastructure Security Agency (CISA) issued an urgent warning: Two newly discovered, critical vulnerabilities in Cisco Identity Services Engine (ISE) are being exploited in the wild. If your organization uses Cisco ISE to secure access and manage user authentication, your risk just shot up.

But what does this really mean for enterprise security teams, and why is the clock ticking? Let’s break down what’s crucial, why it matters, and—most importantly—what you must do right now to protect your network.

What’s Happening: CISA Adds Cisco ISE Vulnerabilities to KEV Catalog

On July 28, CISA added three new vulnerabilities to its Known Exploited Vulnerabilities (KEV) catalog—a notorious list no software vendor wants to see their products on. Two of these, CVE-2025-20281 and CVE-2025-20337, target Cisco ISE, the very backbone of identity-driven network security for thousands of enterprises.

So, why is this a red alert for security teams? Because when a vulnerability lands in KEV, it means real attackers are actively exploiting it—not just running it in labs, but in live environments like yours. And for Cisco ISE users, the implications are massive: attackers can hijack network controls and gain root access, putting the entire organization at risk.

Let’s dive deeper into what these vulnerabilities are, how they work, and why CISA has issued a hard deadline for remediation.

Cisco ISE: The Beating Heart of Enterprise Network Security

Before we get technical, let’s put Cisco ISE into context. Think of it as the “bouncer” at your company’s digital front door. It decides who gets in, what they can do, and keeps a watchful eye to make sure all users and devices are behaving. ISE handles:

Authentication: Verifying user and device identities
Authorization: Granting the appropriate level of access
Accounting (AAA): Logging usage for compliance and auditing

For organizations with complex, distributed networks—think hospitals, universities, or global corporations—ISE acts as both gatekeeper and security command center. That’s why any vulnerability in ISE isn’t just an IT problem—it’s a business risk.

Inside the Threat: CVE-2025-20281 and CVE-2025-20337 Explained

What Makes These Vulnerabilities So Dangerous?

Both issues stem from insufficient input validation in specific APIs within Cisco ISE and its Passive Identity Connector (ISE-PIC). That’s a fancy way of saying: the software doesn’t properly check data sent by users before acting on it.

Here’s why that matters:
Attackers can craft malicious API requests that slip past ISE’s defenses. And since these vulnerabilities can be triggered remotely, without authentication, a would-be hacker doesn’t need special access or insider knowledge.

The result?
If exploited, either vulnerability allows an attacker to execute arbitrary code as root—the highest level of privilege on the system. In practice, this means an attacker can:

Take full control of the Cisco ISE server
Move laterally across your network
Disable security measures, exfiltrate data, or launch further attacks

Both vulnerabilities have been rated with a CVSS v3.1 score of 10.0—the maximum score, signaling “critical” severity.

Affected Versions: Are You at Risk?

Let’s get specific. The following Cisco ISE versions are vulnerable:

3.3.0
3.3 Patch 1
3.3 Patch 2
3.3 Patch 3
3.3 Patch 4
3.3 Patch 5
3.3 Patch 6
3.4.0
3.4 Patch 1

Additionally, CVE-2025-20337 affects Cisco ISE-PIC versions:

3.1.0
3.2.0
3.3.0
3.4.0

If your organization is running any of these, you are directly exposed to active exploitation.

How Attackers Exploit These Cisco ISE Flaws

Let’s demystify the technical jargon.
Picture the ISE API as a set of “doors” into the system—doors that, if left unlocked, can be used by anyone. In this case, researchers from the Trend Micro Zero Day Initiative identified that certain API endpoints in Cisco ISE and ISE-PIC weren’t properly locked down.

Here’s a simplified view of the attack chain:

Remote Discovery: Attackers scan for vulnerable Cisco ISE servers exposed to the internet.
Malicious Request: They craft a special API request with malicious payloads.
Privilege Escalation: The system, lacking proper checks, processes the request, executing the payload as root.
Full Compromise: The attacker now controls the ISE server, with the ability to pivot deeper into the network.

No special credentials required. No need for insider access. Just one unpatched, exposed system.

Cisco’s Response: Patches and No Workarounds

Cisco responded quickly, publishing advisories and releasing patches for all affected ISE and ISE-PIC versions. However, there’s a catch: There are no temporary workarounds. The only way to mitigate these vulnerabilities is to apply Cisco’s official patches.

The Cisco Product Security Incident Response Team (PSIRT) has also confirmed that exploits are happening in real-world environments.

CISA’s Mandate: Patch by August 18—or Face Compliance Issues

Why is CISA’s involvement so significant?
CISA’s KEV catalog is not just a “watch list”—it’s a call to action, particularly for federal agencies and any organization running critical infrastructure. CISA has set an August 18 deadline for organizations to patch or mitigate these vulnerabilities.

Here’s what that means:

If you’re a federal agency or contractor, CISA compliance is mandatory.
Private sector organizations should treat this as a high-priority action item.
(Attackers don’t care about compliance—they go where the opportunity is!)

In short: If you haven’t patched by August 18, you’re not just risking a breach—you may be out of regulatory compliance.

What’s the Real-World Impact? Why Should You Care?

Let’s step out of the technical weeds for a moment.
Imagine your Cisco ISE server as the bank vault controlling access to your digital assets. Now, imagine you discover two holes have appeared in the vault—for weeks, and attackers are already trying to exploit them.

Critical systems at risk: ISE is often integrated with other security tools like firewalls, VPNs, and endpoint security. A compromise here can ripple across your entire security stack.
No authentication needed: Attackers don’t need to guess passwords or phish users—just send the right API call.
Active exploitation: These flaws aren’t theoretical. Exploit attempts are happening now, increasing your risk with every day unpatched.

Action Plan: How to Protect Your Organization

Don’t panic—but do act quickly. Here’s your step-by-step action plan:

1. Identify Affected Systems

Inventory all Cisco ISE and ISE-PIC deployments across your network, including test, backup, and development instances.
Check exact version numbers—even one unpatched system poses a risk.

2. Apply Cisco’s Security Patches

Download official patches from Cisco’s Security Advisory page.
Follow Cisco’s update guidance; schedule downtime if necessary, but don’t delay.

3. Monitor for Signs of Exploitation

Check system logs for suspicious API activity or unexplained changes in configurations.
Use Cisco-provided indicators of compromise (IOCs) if available.

4. Harden Your Network Perimeter

Ensure Cisco ISE servers aren’t unnecessarily exposed to the internet.
Restrict API access to trusted, internal addresses only.

5. Communicate and Document

Notify IT, security, and compliance teams about the urgency and actions taken.
Keep records of patching for regulatory or audit purposes.

Pro Tip:

If you rely on a managed service provider (MSP) for network management, confirm with them directly that these patches have been applied—or insist on written confirmation.

The Third Vulnerability: PaperCut Print Management Software (CVE-2023-2533)

While Cisco ISE is getting the spotlight, CISA’s KEV update also includes CVE-2023-2533, a high-severity CSRF vulnerability in PaperCut NG and MF.

What’s at Stake?

PaperCut NG/MF are used by schools, businesses, and governments to manage printing and document workflows.
The vulnerability allows attackers to trick users into performing unauthorized actions via crafted web requests—potentially leading to data leaks or permission changes.

Who’s Affected?

PaperCut NG/MF versions prior to the patched release.
For details and remediation, consult the official PaperCut security bulletin.

Why Are We Seeing More Critical Infrastructure Attacks?

The rise in KEV-listed vulnerabilities like these isn’t an accident. Attackers target systems that provide maximum leverage—and identity management platforms like Cisco ISE are prime targets. Here’s why:

They control access: Compromising identity infrastructure lets attackers leapfrog other defenses.
High-value, low-visibility: ISE and similar tools are often overlooked in patch management cycles.
Remote exploitation: Flaws that don’t require authentication are irresistible to attackers.

Organizations can’t afford to treat identity infrastructure as “set it and forget it.” Today’s landscape demands continuous vigilance.

Practical Steps for Ongoing Defense

Mitigating these Cisco ISE and PaperCut vulnerabilities is urgent, but it’s also a wake-up call for broader security hygiene:

Establish a routine vulnerability management program.
Follow CISA’s KEV catalog and subscribe to vendor security bulletins.
Prioritize patching for critical systems—identity, authentication, and access controls.
Implement network segmentation: Limit the blast radius if a system is compromised.
Regularly audit and restrict API access and privileges.

Remember, attackers exploit gaps in process as much as they exploit code flaws.

Frequently Asked Questions (FAQ)

What is Cisco Identity Services Engine (ISE), and why is it important?

Cisco ISE is a network security platform that manages user and device authentication, authorization, and accounting (AAA) to control network access. It’s critical because it acts as a gatekeeper, ensuring only authorized users and devices can access your systems.

What are CVE-2025-20281 and CVE-2025-20337?

These are critical vulnerabilities in Cisco ISE (and ISE-PIC) identified by security researchers. Both allow unauthenticated, remote attackers to execute code as root, potentially giving them total control of affected systems.

Are these Cisco ISE vulnerabilities being exploited in the wild?

Yes. Cisco and CISA have confirmed active exploitation attempts. That’s why they’re listed in the CISA Known Exploited Vulnerabilities (KEV) catalog and why urgent patching is required.

How do I know if my organization is affected?

Check if any of your Cisco ISE or ISE-PIC systems are running the versions listed above. If so, you need to apply patches immediately.

Can I simply disable the affected APIs or use a workaround?

No official workaround exists. Cisco’s only recommended mitigation is to apply the latest security patches.

What is CISA’s Known Exploited Vulnerabilities (KEV) catalog?

The KEV catalog is a list of vulnerabilities known to be actively exploited by threat actors. CISA uses it to drive Federal—and recommended private sector—remediation efforts.

What is CVE-2023-2533 in PaperCut?

This is a high-severity cross-site request forgery (CSRF) vulnerability in PaperCut NG and MF print management software. It can let attackers trick users into performing unauthorized actions.

Where can I find more details or get updates?

Cisco Security Advisories: Cisco Security Center
CISA KEV Catalog: CISA KEV
PaperCut Security Bulletins: PaperCut Security

Final Takeaway: Secure Your Identity Infrastructure—Now

If you take away one thing, let it be this: critical vulnerabilities in identity infrastructure like Cisco ISE represent a clear and present danger. Attackers are already at the gates, and the only way to keep them out is to patch—immediately.

Don’t wait for August 18. The best time to secure your network was yesterday; the second-best time is now.
Keep your defenses sharp, your systems updated, and your teams informed.

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Stay safe—and stay patched!

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CISA Alert: Critical Cisco ISE Vulnerabilities Under Active Attack—Here’s What Enterprises Must Know and Do Now

What’s Happening: CISA Adds Cisco ISE Vulnerabilities to KEV Catalog

Cisco ISE: The Beating Heart of Enterprise Network Security

Inside the Threat: CVE-2025-20281 and CVE-2025-20337 Explained