Amazon alerts: advanced threat actor exploits Cisco ISE & Citrix NetScaler zero
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2025-20337 | Unauthenticated Injection Flaw Allows Root RCE in Cisco ISE and ISE-PIC CVE-2025-20337 is a critical (CVSS 3.1: 10.0) injection vulnerability (CWE-74) in a specific API of Cisco Identity Services Engine (ISE) and Cisco ISE Passive Identity Connector (ISE-PIC), caused by insufficient validation of user-supplied input. An unauthenticated, remote attacker can trigger it by submitting a crafted request to the affected API, with no valid credentials required. Successful exploitation allows arbitrary code execution on the underlying operating system with root privileges, giving the attacker full control of the affected device, consistent with the changed-scope, high-impact CVSS score. Any organization running Cisco ISE or ISE-PIC is potentially affected; CISA added the flaw to the Known Exploited Vulnerabilities catalog on 2025-07-28, and press reports indicate active exploitation, including zero-day use per Amazon threat intelligence coverage. EPSS assigns a 67% probability of exploitation within 30 days (99th percentile), and no public proof-of-concept is known. Do: Upgrade Cisco ISE and ISE-PIC to the fixed releases identified in Cisco's security advisory (fixed version details are not included in this data set), and check management/API logs for unauthenticated crafted API requests indicating exploitation. As an interim mitigation, restrict network access to the affected API and the ISE administration interface. Organizations covered by BOD 22-01 must apply vendor mitigations per Cisco's instructions or discontinue use of the product by the KEV remediation deadline. | 10.0 | 68% | KEV |
| moderatelikely on the order of tens of thousands of enterprise deployments worldwide (deployment-pattern estimate; no public install or scan counts) | |
| CVE-2025-5777 | Out-of-Bounds Read (Memory Overread) in Citrix NetScaler ADC and Gateway Citrix NetScaler ADC and NetScaler Gateway contain an out-of-bounds read (CWE-125) caused by insufficient input validation, which can cause the appliance to read beyond the intended memory buffer (a memory overread). The flaw is only triggerable when the appliance is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, or RDP Proxy) or as an AAA virtual server, so attackers who can reach those services can potentially induce the overread and obtain sensitive memory contents. Such disclosure could aid follow-on compromise, for example by exposing session or authentication data, and CISA notes known ransomware use. Organizations running NetScaler ADC or NetScaler Gateway in the affected Gateway/AAA configurations are exposed. The vulnerability was added to CISA's Known Exploited Vulnerabilities catalog on 2025-07-10 with known ransomware use and an EPSS of 100% (100th percentile), indicating active exploitation, while no public PoC is known and a CVSS score has not yet been assigned. Do: Apply the fixed NetScaler ADC/Gateway builds per Citrix's security advisory (exact affected/fixed version ranges are not in the available data, so consult the bulletin); per CISA KEV, apply vendor mitigations, follow BOD 22-01 guidance for cloud services, or discontinue use if mitigations are unavailable. Inventory appliances for Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server configurations, since unconfigured/other deployments are not triggerable. After patching, terminate active and idle VPN sessions and hunt for anomalous access, given the known ransomware exploitation and the information-disclosure nature of the flaw. | 9.3 | 100% | KEV ransomware |
| massplausibly hundreds of thousands of installed/internet-exposed NetScaler ADC and Gateway appliances (public scans have historically shown on the order of… |
Full article341 words · extracted from securityaffairs.com · click to collapse
Pierluigi Paganini
November 13, 2025
Amazon warns that an advanced threat actor exploited zero-days in Cisco ISE and Citrix NetScaler to deploy custom malware.
Amazon’s threat intelligence researchers spotted an advanced threat actor exploiting two previously undisclosed zero-day flaws in Cisco Identity Service Engine (ISE) and Citrix NetScaler ADC to deliver custom malware.
Attackers also exploited multiple undisclosed vulnerabilities.
Amazon’s honeypots revealed exploitation attempts of the Citrix Bleed Two (CVE-2025-5777) and Cisco ISE (CVE-2025-20337) for pre-auth RCE before public disclosure.
“What made this discovery particularly concerning was that exploitation was occurring in the wild before Cisco had assigned a CVE number or released comprehensive patches across all affected branches of Cisco ISE.” reads the advisory published by Amazon. “This patch-gap exploitation technique is a hallmark of sophisticated threat actors who closely monitor security updates and quickly weaponize vulnerabilities.”
One exploited Cisco ISE, the actor installed a bespoke web shell masquerading as IdentityAuditAction. Built for ISE, it ran fully in-memory, injected via Java reflection, and registered an HTTP listener on Tomcat.
“This wasn’t typical off-the-shelf malware, but rather a custom-built backdoor specifically designed for Cisco ISE environments.” states the report.
The web shell used DES with nonstandard Base64, required specific headers for access, and left minimal artifacts. The deserialization routine decoded a payload, defined or instantiated a proxy class, and executed it. The actor showed expert knowledge of Java, Tomcat, and Cisco ISE internals, suggesting a well-funded group with access to multiple zero-days and advanced exploit research.
Amazon security researchers warn that critical infrastructure, including identity systems and remote access gateways, are prime targets. Even well-maintained systems are at risk, highlighting the need for defense-in-depth, robust detection, and restricted access to privileged endpoints.
“The pre-authentication nature of these exploits reveals that even well-configured and meticulously maintained systems can be affected.” concludes the report. “This underscores the importance of implementing comprehensive defense-in-depth strategies and developing robust detection capabilities that can identify unusual behavior patterns.”
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