CVE-2020-36477Network attack vector

Server impersonation via subjectAltName type confusion

Published Aug 23, 2021 · Updated Aug 4, 2024

Improper certificate validation in Mbed TLS before 2.24.0 allows remote attackers to impersonate selected domain names. mbedtls_x509_crt_verify compares the expected hostname byte-for-byte against every subjectAltName entry without checking its name type. Exploitation requires control of the IPv4 or IPv6 address whose raw bytes equal a 4-byte or 16-byte hostname, enabling acceptance of an attacker-controlled certificate.

CVSS severity5.9
Medium
EPSS probability0.86%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Mbed TLS before 2.24.0 allows remote attackers to impersonate selected domain names. mbedtls_x509_crt_verify compares the expected hostname byte-for-byte against every subjectAltName entry without checking its name type. Exploitation requires control of the IPv4 or IPv6 address whose raw bytes equal a 4-byte or 16-byte hostname, enabling acceptance of an attacker-controlled certificate.

The record

CVE
CVE-2020-36477
Published
Aug 23, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 23, 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

4.3NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:N/I:P/A:N
5.9NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/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-295Improper Certificate Validation
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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