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CVE-2021-36647

4.7 · MEDIUM

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…

Published Jan 17, 2023CWE-327EPSS 0.16%

Overview

CVE-2021-36647 is a medium-severity vulnerability. It was published on January 17, 2023 and has a CVSS 3.1 base score of 4.7 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 4.7, rated MEDIUM. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/ARMmbed/mbedtls/releases/Refkouzili.com/Load-Step.pdfReftls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2021-07-1GitHubgithub.com/ARMmbed/mbedtls/releases/Refkouzili.com/Load-Step.pdfReflists.debian.org/debian-lts-announce/2025/06/msg00034.htmlReftls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2021-07-1

How CyberStrike helps

Frequently asked questions

What is CVE-2021-36647?

CVE-2021-36647 is a medium-severity vulnerability. It was published on January 17, 2023 and has a CVSS 3.1 base score of 4.7 (MEDIUM).

How severe is CVE-2021-36647?

This vulnerability has a CVSS 3.1 base score of 4.7, rated MEDIUM. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2021-36647?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-36647?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-36647 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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