
Zyxel GS1900 Zero-Day: How a Faulty Patch Left 996 Switches Open to Root Takeover by Red Heron
In August 2026, a Chinese-speaking threat actor tracked as Red Heron exploited an unauthenticated remote code execution vulnerability in Zyxel GS1900-series managed switches to harvest configuration data, hashed root credentials, and network topology details from 996 devices. The attackers leveraged an out-of-bounds write flaw (CVE-2026-107441) in the switch's web management handler—a flaw that Zyxel's earlier Patch 2 firmware (CVE-2026-7273) failed to fully remediate because the size check was applied after the malicious parameter had already been copied into memory. Commands executed with root privileges. Zyxel released Patch 3 firmware across ten GS1900 models on October 23, 2026, providing the authoritative fix. This incident exposes a persistent and dangerous pattern: vendor patches that address a symptom while leaving the underlying memory-safety defect exploitable. With CISA's KEV catalog still not listing CVE-2026-107441 as of early November 2026, organizations that believed they were protected by Patch 2 remain silently exposed—underscoring the risk of trusting patch compliance alone without runtime network controls.
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