CVE-2021-36647

low-risk
Published 2023-01-17

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.

Do I need to act?

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0.04% chance of exploitation
EPSS score — low exploit probability
-
Not on CISA KEV list
No confirmed active exploitation reported to CISA
?
Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
4
CVSS 4.7/10 Medium
LOCAL / HIGH complexity

Affected Products (1)

Affected Vendors

Arm

References (7)

Third Party Advisory https://github.com/ARMmbed/mbedtls/releases/
Third Party Advisory https://kouzili.com/Load-Step.pdf
Vendor Advisory https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-...
Third Party Advisory https://github.com/ARMmbed/mbedtls/releases/
Third Party Advisory https://kouzili.com/Load-Step.pdf
https://lists.debian.org/debian-lts-announce/2025/06/msg00034.html
Vendor Advisory https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-...
17
/ 100
low-risk
Severity 12/34 · Low
Exploitability 0/34 · Minimal
Exposure 5/34 · Minimal