CVE-2021-36647: Arm Mbed TLS

Medium severity, CVSS 4.7. EPSS: 0.2% chance of exploitation in the next 30 days.

Use of a Broken or Risky Cryptographic Algorithm in the function mbedtls_mpi_exp_mod() in lignum.c in Mbed TLS Mbed TLS all versions before 3.0.0, 2.27.0 or 2.16.11 allows attackers with access to precise enough timing and memory access information (typically an untrusted operating system attacking a secure enclave such as SGX or the TrustZone secure world) to recover the private keys used in RSA.

Affected products

• Arm Mbed TLS: before 2.16.11 (fixed in 2.16.11); from 2.17.0, before 2.27.0 (fixed in 2.27.0)
• Trustedfirmware Mbed TLS: from 2.28.0, before 3.0.0 (fixed in 3.0.0)

Published 2023-01-17. Last modified 2026-06-17.