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Vulnerability record · CVE-2021-23841 · published 16 February 2021

CVE-2021-23841: Openssl null pointer dereference vulnerability

OOpenssl · Openssl

The OpenSSL public API function X509_issuer_and_serial_hash() attempts to create a unique hash value based on the issuer and serial number data contained within an X509 certificate. However it fails to correctly handle any errors that may occur while parsing the issuer field (which might occur if the issuer field is maliciously constructed). This may subsequently result in a NULL pointer deref and a crash leading to a potential denial of service attack. The function X509_issuer_and_serial_hash() is never directly called by OpenSSL itself so applications are only vulnerable if they use this function directly and they use it on certificates that may have been obtained from untrusted sources. OpenSSL versions 1.1.1i and below are affected by this issue. Users of these versions should upgrade to OpenSSL 1.1.1j. OpenSSL versions 1.0.2x and below are affected by this issue. However OpenSSL 1.0.2 is out of support and no longer receiving public updates. Premium support customers of OpenSSL 1.0.2 should upgrade to 1.0.2y. Other users should upgrade to 1.1.1j. Fixed in OpenSSL 1.1.1j (Affected 1.1.1-1.1.1i). Fixed in OpenSSL 1.0.2y (Affected 1.0.2-1.0.2x).

5.9 CVSS 3.1 Medium EPSS 7.4% · top 5.8% CWE-476 · NULL pointer dereference
5.9CVSS 3.1 base score, v2 4.3
7.4%EPSS exploitation probability, 30 days
NoNot in CISA KEV
23Affected product versions listed by NVD
44References
17 Jun 2026Last modified by NVD

Description

The OpenSSL public API function X509_issuer_and_serial_hash() attempts to create a unique hash value based on the issuer and serial number data contained within an X509 certificate. However it fails to correctly handle any errors that may occur while parsing the issuer field (which might occur if the issuer field is maliciously constructed). This may subsequently result in a NULL pointer deref and a crash leading to a potential denial of service attack. The function X509_issuer_and_serial_hash() is never directly called by OpenSSL itself so applications are only vulnerable if they use this function directly and they use it on certificates that may have been obtained from untrusted sources. OpenSSL versions 1.1.1i and below are affected by this issue. Users of these versions should upgrade to OpenSSL 1.1.1j. OpenSSL versions 1.0.2x and below are affected by this issue. However OpenSSL 1.0.2 is out of support and no longer receiving public updates. Premium support customers of OpenSSL 1.0.2 should upgrade to 1.0.2y. Other users should upgrade to 1.1.1j. Fixed in OpenSSL 1.1.1j (Affected 1.1.1-1.1.1i). Fixed in OpenSSL 1.0.2y (Affected 1.0.2-1.0.2x).

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

23 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://seclists.org/fulldisclosure/2021/May/67 Mailing ListThird Party Advisory
http://seclists.org/fulldisclosure/2021/May/68 Mailing ListThird Party Advisory
http://seclists.org/fulldisclosure/2021/May/70 Mailing ListThird Party Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-637483.pdf PatchThird Party Advisory
https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=122a19ab48091c657f7cb1fb3af9fc07bd557bbf
https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=8252ee4d90f3f2004d3d0aeeed003ad49c9a7807
https://kb.pulsesecure.net/articles/Pulse_Security_Advisories/SA44846 Third Party Advisory
https://security.gentoo.org/glsa/202103-03 Third Party Advisory
https://security.netapp.com/advisory/ntap-20210219-0009/ Third Party Advisory
https://security.netapp.com/advisory/ntap-20210513-0002/ Third Party Advisory
https://security.netapp.com/advisory/ntap-20240621-0006/
https://support.apple.com/kb/HT212528 Third Party Advisory
https://support.apple.com/kb/HT212529 Third Party Advisory
https://support.apple.com/kb/HT212534 Third Party Advisory
https://www.debian.org/security/2021/dsa-4855 Third Party Advisory
https://www.openssl.org/news/secadv/20210216.txt Vendor Advisory
https://www.oracle.com//security-alerts/cpujul2021.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpuApr2021.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html PatchThird Party Advisory
https://www.tenable.com/security/tns-2021-03 Third Party Advisory
https://www.tenable.com/security/tns-2021-09 Third Party Advisory
http://seclists.org/fulldisclosure/2021/May/67 Mailing ListThird Party Advisory
http://seclists.org/fulldisclosure/2021/May/68 Mailing ListThird Party Advisory
http://seclists.org/fulldisclosure/2021/May/70 Mailing ListThird Party Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-637483.pdf PatchThird Party Advisory
https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=122a19ab48091c657f7cb1fb3af9fc07bd557bbf
https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=8252ee4d90f3f2004d3d0aeeed003ad49c9a7807
https://kb.pulsesecure.net/articles/Pulse_Security_Advisories/SA44846 Third Party Advisory
https://security.gentoo.org/glsa/202103-03 Third Party Advisory
https://security.netapp.com/advisory/ntap-20210219-0009/ Third Party Advisory
https://security.netapp.com/advisory/ntap-20210513-0002/ Third Party Advisory
https://security.netapp.com/advisory/ntap-20240621-0006/
https://support.apple.com/kb/HT212528 Third Party Advisory
https://support.apple.com/kb/HT212529 Third Party Advisory
https://support.apple.com/kb/HT212534 Third Party Advisory
https://www.debian.org/security/2021/dsa-4855 Third Party Advisory
https://www.openssl.org/news/secadv/20210216.txt Vendor Advisory
https://www.oracle.com//security-alerts/cpujul2021.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpuApr2021.html PatchThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-23841), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.