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Amazon Says Zero-Day Attacks Hit Citrix NetScaler and Cisco ISE, Dropping Stealthy Custom Web Shell

Pre-disclosure exploitation of edge identity flaws underscores the need for rapid patching plus restricted access.

Overview

  • Amazon's MadPot detected pre-disclosure exploitation of Citrix Bleed 2 (CVE-2025-5777), confirming zero-day use.
  • Investigators linked the same threat to Cisco ISE CVE-2025-20337 and observed deployment of a bespoke in-memory web shell named IdentityAuditAction.
  • The backdoor injected with Java reflection, monitored all Tomcat HTTP requests, and used DES with non-standard Base64 to minimize traces.
  • Amazon traced Cisco ISE exploitation to May and June, prior to Cisco's late-June advisory and subsequent July warnings.
  • Vendors issued patches in June–July 2025, CISA flagged active exploitation, and organizations are urged to update and restrict exposure of management portals.