CVE-2021-27562

Arm Trusted Firmware-M (TF-M), the open-source reference secure firmware for Cortex-M microcontrollers with TrustZone, through version 1.2 contains an out-of-bounds write (CWE-787) in the non-secure processing environment (NSPE) handler-mode path. The flaw is triggered when software running in the non-secure world calls a secure function while in handler mode, which can corrupt memory or secure state. A successful trigger can halt the system, overwrite secure data, or print secure data to output; the scored impact is high availability (CVSS 3.1: 5.5, AV:L/PR:L), so exploitation requires local code execution in the non-secure world. Any device whose firmware is built on TF-M 1.2 or earlier is affected, spanning the many silicon vendors and IoT products that ship Arm's reference secure firmware. The flaw is listed in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating known exploitation in the wild, though no public PoC is documented and ransomware use is unknown.

What to do: Apply updates per vendor instructions: device makers and OEMs should rebuild firmware on a TF-M release newer than 1.2, and device owners should install updated firmware/SDKs from their silicon vendor or OEM. Check which of your microcontroller-based products (e.g., IoT endpoints) use Trusted Firmware-M and whether they run third-party or non-secure applications that could invoke secure functions; because exploitation requires local code execution, prioritize devices accepting remote code or app deployment. Containment is not otherwise available, as the fix is in the secure firmware itself.