CVE-2021-36647

RSA private-key recovery via secret-dependent memory access

Published Jan 17, 2023 · Updated Nov 3, 2025

Side-channel leakage in Mbed TLS before 3.0.0, 2.27.0, or 2.16.11 allows local users to recover RSA private keys. The sliding-window modular exponentiation in mbedtls_mpi_exp_mod performs secret-dependent memory accesses; one precisely observed RSA operation defeats exponent blinding. Exploitation requires precise timing and memory-access visibility, typically from an untrusted OS observing SGX or TrustZone enclave execution, and exposes RSA private keys without modifying data.

CVSS severity4.7
Medium
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Side-channel leakage in Mbed TLS before 3.0.0, 2.27.0, or 2.16.11 allows local users to recover RSA private keys. The sliding-window modular exponentiation in mbedtls_mpi_exp_mod performs secret-dependent memory accesses; one precisely observed RSA operation defeats exponent blinding. Exploitation requires precise timing and memory-access visibility, typically from an untrusted OS observing SGX or TrustZone enclave execution, and exposes RSA private keys without modifying data.

The record

CVE
CVE-2021-36647
Published
Jan 17, 2023
Updated
Nov 3, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-327
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 17, 2023CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.7GitHub Advisory DatabaseCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-327Use of a Broken or Risky Cryptographic Algorithm

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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