CVE-2020-36478Public exploitNetwork attack vector

Invalid certificate acceptance via omitted ASN.1 tag check

Published Aug 23, 2021 · Updated Aug 4, 2024

Improper certificate validation in Arm Mbed TLS before 2.25.0 allows remote attackers to obtain acceptance of invalid X.509 certificates. The X.509 parser compares signature algorithm parameters by length and content but omits their ASN.1 tags, treating distinct zero-length parameter types as equal. Exploitation requires an application to validate an attacker-supplied certificate with mismatched algorithm parameter tags, undermining the application's certificate-based trust decision.

CVSS severity7.5
High
EPSS probability1.18%
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 Arm Mbed TLS before 2.25.0 allows remote attackers to obtain acceptance of invalid X.509 certificates. The X.509 parser compares signature algorithm parameters by length and content but omits their ASN.1 tags, treating distinct zero-length parameter types as equal. Exploitation requires an application to validate an attacker-supplied certificate with mismatched algorithm parameter tags, undermining the application's certificate-based trust decision.

The record

CVE
CVE-2020-36478
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

7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.0NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:P/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

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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