CVE-2021-3450Network attack vector

Certificate subject impersonation via overwritten CA check

Published Mar 25, 2021 · Updated Sep 17, 2024

Improper certificate validation in OpenSSL 1.1.1h through 1.1.1j allows remote attackers to impersonate certificate subjects via a forged chain. In crypto/x509/x509_vfy.c, check_chain_extensions() lets check_curve() overwrite an earlier invalid-CA result, so a non-CA certificate can issue another certificate. Exploitation requires an application to enable X509_V_FLAG_X509_STRICT and leave the verification purpose unset or override libssl's default purpose, permitting acceptance of a forged issuer chain.

CVSS severity7.4
High
EPSS probability18.34%
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 OpenSSL 1.1.1h through 1.1.1j allows remote attackers to impersonate certificate subjects via a forged chain. In crypto/x509/x509_vfy.c, check_chain_extensions() lets check_curve() overwrite an earlier invalid-CA result, so a non-CA certificate can issue another certificate. Exploitation requires an application to enable X509_V_FLAG_X509_STRICT and leave the verification purpose unset or override libssl's default purpose, permitting acceptance of a forged issuer chain.

The record

CVE
CVE-2021-3450
Published
Mar 25, 2021
Updated
Sep 17, 2024
Vendor
OpenSSL Project
Product
OpenSSL
Classifications
CWE-295
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Fixed in OpenSSL 1.1.1k (Affected 1.1.1h-1.1.1j)

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenSSL Project · OpenSSLversion=Fixed in OpenSSL 1.1.1k (Affected 1.1.1h-1.1.1j)

Published CVSS scores

7.4GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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.

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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 exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation

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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