CVE-2021-23841 | Null pointer deref in X509_issuer_and_serial_hash()

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).

Published: 2021-02-16 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]

Conclusion & alert: CVE-2021-23841 is rated Moderate Risk (61.4/100): CVSS Medium severity, with high exploitation likelihood (EPSS 7.47%, 94th percentile). Core evidence: EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +6.51% over the last day, indicating growing attacker interest. Mandatory action: High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-23841

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.96% 7.47% +6.51%
2 2026-04-20 0.66% 0.96% +0.29%
3 2026-03-18 0.66%

Full EPSS history (38 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-23841

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
2.2 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-23841

GitHub Security Advisory for CVE-2021-23841

GHSA-84rm-qf37-fgc2 · Severity: medium · Ecosystem: rust — Integer Overflow in openssl-src

OS Trackers for CVE-2021-23841

vendor priority summary link
alpine medium CVE-2021-23841: 3 source package rows (openssl, openssl1.1-compat, openssl3); 15 state rows across 13 repos (3.10-main, 3.11-main, 3.12-main, 3.17-community, 3.17-main, 3.18-community, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-community, edge-main); fixed 15, open 0. https://security.alpinelinux.org/vuln/CVE-2021-23841
debian not yet assigned CVE-2021-23841 not yet assigned priority: Debian including 1 source packages (openssl), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-23841
gentoo normal CVE-2021-23841: 1 GLSA(s) (202103-03), 1 atom(s) (dev-libs/openssl); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-23841
redhat medium https://access.redhat.com/security/cve/CVE-2021-23841
suse medium CVE-2021-23841 severity moderate: SUSE including 606 source package names (0.1.0:libopenssl1_1-1.1.0i-14.15.1, 0.1.75:libopenssl1_1-1.1.0i-14.15.1, …), 1235 product×package rows across 267 product lines (Container bci/bci-init, Container bci/dotnet-aspnet, … (267 product lines)): Fixed 1041, Known Affected 135, Known Not Affected 59. https://www.suse.com/security/cve/CVE-2021-23841/
ubuntu medium CVE-2021-23841 medium priority: Ubuntu including 4 source packages (edk2, nodejs, openssl, openssl1.0), 24 status rows across 6 suites (bionic, focal, groovy, trusty, upstream, xenial): not-affected 9, released 8, DNE 5, needs-triage 2. https://ubuntu.com/security/CVE-2021-23841

Affected software / configurations for CVE-2021-23841

Vendor Product Version Raw CPE
openssl openssl >= 1.0.2, < 1.0.2y cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 1.1.1, < 1.1.1j cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
tenable nessus_network_monitor 5.11.0 cpe:2.3:a:tenable:nessus_network_monitor:5.11.0:*:*:*:*:*:*:*
tenable nessus_network_monitor 5.11.1 cpe:2.3:a:tenable:nessus_network_monitor:5.11.1:*:*:*:*:*:*:*
tenable nessus_network_monitor 5.12.0 cpe:2.3:a:tenable:nessus_network_monitor:5.12.0:*:*:*:*:*:*:*
tenable nessus_network_monitor 5.12.1 cpe:2.3:a:tenable:nessus_network_monitor:5.12.1:*:*:*:*:*:*:*
tenable nessus_network_monitor 5.13.0 cpe:2.3:a:tenable:nessus_network_monitor:5.13.0:*:*:*:*:*:*:*
tenable tenable.sc >= 5.13.0, <= 5.17.0 cpe:2.3:a:tenable:tenable.sc:*:*:*:*:*:*:*:*
apple safari < 14.1.1 cpe:2.3:a:apple:safari:*:*:*:*:*:*:*:*
apple ipados < 14.6 cpe:2.3:o:apple:ipados:*:*:*:*:*:*:*:*
apple iphone_os < 14.6 cpe:2.3:o:apple:iphone_os:*:*:*:*:*:*:*:*
apple macos >= 11.1, < 11.4 cpe:2.3:o:apple:macos:*:*:*:*:*:*:*:*
netapp oncommand_insight cpe:2.3:a:netapp:oncommand_insight:-:*:*:*:*:*:*:*
netapp oncommand_workflow_automation cpe:2.3:a:netapp:oncommand_workflow_automation:-:*:*:*:*:*:*:*
netapp snapcenter cpe:2.3:a:netapp:snapcenter:-:*:*:*:*:*:*:*
oracle business_intelligence 5.5.0.0.0 cpe:2.3:a:oracle:business_intelligence:5.5.0.0.0:*:*:*:enterprise:*:*:*
oracle business_intelligence 5.9.0.0.0 cpe:2.3:a:oracle:business_intelligence:5.9.0.0.0:*:*:*:enterprise:*:*:*
oracle business_intelligence 12.2.1.3.0 cpe:2.3:a:oracle:business_intelligence:12.2.1.3.0:*:*:*:enterprise:*:*:*
oracle business_intelligence 12.2.1.4.0 cpe:2.3:a:oracle:business_intelligence:12.2.1.4.0:*:*:*:enterprise:*:*:*
oracle communications_cloud_native_core_policy 1.15.0 cpe:2.3:a:oracle:communications_cloud_native_core_policy:1.15.0:*:*:*:*:*:*:*
oracle enterprise_manager_for_storage_management 13.4.0.0 cpe:2.3:a:oracle:enterprise_manager_for_storage_management:13.4.0.0:*:*:*:*:*:*:*
oracle enterprise_manager_ops_center 12.4.0.0 cpe:2.3:a:oracle:enterprise_manager_ops_center:12.4.0.0:*:*:*:*:*:*:*
oracle essbase 21.2 cpe:2.3:a:oracle:essbase:21.2:*:*:*:*:*:*:*
oracle graalvm 19.3.5 cpe:2.3:a:oracle:graalvm:19.3.5:*:*:*:enterprise:*:*:*
oracle graalvm 20.3.1.2 cpe:2.3:a:oracle:graalvm:20.3.1.2:*:*:*:enterprise:*:*:*
oracle graalvm 21.0.0.2 cpe:2.3:a:oracle:graalvm:21.0.0.2:*:*:*:enterprise:*:*:*
oracle jd_edwards_world_security a9.4 cpe:2.3:a:oracle:jd_edwards_world_security:a9.4:*:*:*:*:*:*:*
oracle mysql_enterprise_monitor < 8.0.23 cpe:2.3:a:oracle:mysql_enterprise_monitor:*:*:*:*:*:*:*:*
oracle mysql_server < 5.7.33 cpe:2.3:a:oracle:mysql_server:*:*:*:*:*:*:*:*
oracle mysql_server >= 8.0.15, < 8.0.23 cpe:2.3:a:oracle:mysql_server:*:*:*:*:*:*:*:*
oracle peoplesoft_enterprise_peopletools 8.57 cpe:2.3:a:oracle:peoplesoft_enterprise_peopletools:8.57:*:*:*:*:*:*:*
oracle peoplesoft_enterprise_peopletools 8.58 cpe:2.3:a:oracle:peoplesoft_enterprise_peopletools:8.58:*:*:*:*:*:*:*
oracle peoplesoft_enterprise_peopletools 8.59 cpe:2.3:a:oracle:peoplesoft_enterprise_peopletools:8.59:*:*:*:*:*:*:*
oracle zfs_storage_appliance_kit 8.8 cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*
siemens sinec_ins < 1.0 cpe:2.3:a:siemens:sinec_ins:*:*:*:*:*:*:*:*
siemens sinec_ins 1.0 cpe:2.3:a:siemens:sinec_ins:1.0:-:*:*:*:*:*:*
siemens sinec_ins 1.0 cpe:2.3:a:siemens:sinec_ins:1.0:sp1:*:*:*:*:*:*

References for CVE-2021-23841

URL Tags
http://seclists.org/fulldisclosure/2021/May/67 Mailing List Third Party Advisory
http://seclists.org/fulldisclosure/2021/May/68 Mailing List Third Party Advisory
http://seclists.org/fulldisclosure/2021/May/70 Mailing List Third Party Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-637483.pdf Patch Third 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 Patch Third Party Advisory
https://www.oracle.com/security-alerts/cpuApr2021.html Patch Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html Patch Third Party Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html Patch Third Party Advisory
https://www.tenable.com/security/tns-2021-03 Third Party Advisory
https://www.tenable.com/security/tns-2021-09 Third Party Advisory
cvelogic Threat Intelligence