CVE-2021-36647

Name: CVE-2021-36647
Creator: NVD / NIST
Published: 2023-01-17T21:15:10.88+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.7/10EPSS 0.16%

Last modified Jun 17, 2026

CVE-2021-36647 is a medium-severity vulnerability rated 4.7/10 on the CVSS scale. 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.. EPSS estimates a 0.16% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1

4.7/10

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS Probability

0.16%

5.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Arm	Mbed Tls	< 2.16.11
Arm	Mbed Tls	>= 2.17.0, < 2.27.0
Trustedfirmware	Mbed Tls	>= 2.28.0, < 3.0.0

References

https://github.com/ARMmbed/mbedtls/releases/Third Party Advisory
https://kouzili.com/Load-Step.pdfThird Party Advisory
https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2021-07-1Vendor Advisory
https://github.com/ARMmbed/mbedtls/releases/Third Party Advisory
https://kouzili.com/Load-Step.pdfThird Party Advisory
https://lists.debian.org/debian-lts-announce/2025/06/msg00034.html
https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2021-07-1Vendor Advisory

Timeline

Published: Jan 17, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-36647?

How severe is CVE-2021-36647?

CVE-2021-36647 has a CVSS score of 4.7/10 (MEDIUM severity). The EPSS model estimates a 0.16% probability of exploitation in the next 30 days.

How do I fix CVE-2021-36647?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-36647?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST