CVE-2020-36423Network attack vector

Plaintext recovery via hardware-accelerated Lucky 13

Published Jul 19, 2021 · Updated Aug 4, 2024

Timing side channel in Arm Mbed TLS before 2.23.0 allows remote attackers to recover TLS plaintext through repeated timing measurements. The CBC record-decryption path applies ineffective Lucky 13 timing equalization when MBEDTLS_SHAxxx_ALT selects a hardware-accelerated hash implementation. Exploitation requires an active network position, CBC ciphersuites, hardware-accelerated SHA, repeated measurements, and repeatedly exposed secret plaintext.

CVSS severity7.5
High
EPSS probability1.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Timing side channel in Arm Mbed TLS before 2.23.0 allows remote attackers to recover TLS plaintext through repeated timing measurements. The CBC record-decryption path applies ineffective Lucky 13 timing equalization when MBEDTLS_SHAxxx_ALT selects a hardware-accelerated hash implementation. Exploitation requires an active network position, CBC ciphersuites, hardware-accelerated SHA, repeated measurements, and repeatedly exposed secret plaintext.

The record

CVE
CVE-2020-36423
Published
Jul 19, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-319, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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 vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-319Cleartext Transmission of Sensitive Information
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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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