CVE-2020-36421Public exploit

RSA private-key disclosure via secret-dependent branching

Published Jul 19, 2021 · Updated Dec 3, 2025

Side-channel information disclosure in Arm Mbed TLS before 2.23.0 allows local users to recover RSA private keys from secure enclaves. The mpi_montmul routine branches on secret-dependent comparison results, letting interrupt-resume timing reveal the control-flow path taken during modular exponentiation. Exploitation requires OS-level control of precise interrupts against an SGX enclave and enough observations to reconstruct the enclave's RSA key.

CVSS severity5.3
Medium
EPSS probability1.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Side-channel information disclosure in Arm Mbed TLS before 2.23.0 allows local users to recover RSA private keys from secure enclaves. The mpi_montmul routine branches on secret-dependent comparison results, letting interrupt-resume timing reveal the control-flow path taken during modular exponentiation. Exploitation requires OS-level control of precise interrupts against an SGX enclave and enough observations to reconstruct the enclave's RSA key.

The record

CVE
CVE-2020-36421
Published
Jul 19, 2021
Updated
Dec 3, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-203, T1552.004
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Jul 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Dec 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 privilegesadmin

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-203Observable Discrepancy
T1552.004Private Keys

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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