CVE-2021-23841Network attack vector

Application crash via unchecked issuer parse failure

Published Feb 16, 2021 · Updated Sep 16, 2024

NULL pointer dereference in OpenSSL 1.0.2 through 1.0.2x and 1.1.1 through 1.1.1i allows remote attackers to crash applications. In X509_issuer_and_serial_hash(), X509_NAME_oneline() can return NULL for a malformed issuer, but the unchecked pointer reaches strlen() during digest input processing. Exposure requires an application to call this API directly on a certificate from an untrusted source; a crafted issuer can terminate that application.

CVSS severity5.9
Medium
EPSS probability7.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in OpenSSL 1.0.2 through 1.0.2x and 1.1.1 through 1.1.1i allows remote attackers to crash applications. In X509_issuer_and_serial_hash(), X509_NAME_oneline() can return NULL for a malformed issuer, but the unchecked pointer reaches strlen() during digest input processing. Exposure requires an application to call this API directly on a certificate from an untrusted source; a crafted issuer can terminate that application.

The record

CVE
CVE-2021-23841
Published
Feb 16, 2021
Updated
Sep 16, 2024
Vendor
OpenSSL Project
Product
OpenSSL
Classifications
CWE-476, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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 1.0.2y (Affected 1.0.2-1.0.2x)
  2. Affected versionversion=Fixed in OpenSSL 1.1.1j (Affected 1.1.1-1.1.1i)

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenSSL Project · OpenSSLversion=Fixed in OpenSSL 1.0.2y (Affected 1.0.2-1.0.2x); version=Fixed in OpenSSL 1.1.1j (Affected 1.1.1-1.1.1i)

Published CVSS scores

5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

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-476NULL Pointer Dereference
T1499.004Application or System Exploitation

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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