CVE-2021-23841: Null pointer deref in X509_issuer_and_serial_hash()
Noroxi assessment
Priority: Monitor (action score 25/100)
- Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
- Probability of exploitation in the next 30 days: 7.4% (FIRST EPSS); higher than 94.4% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- Fixed version: edk2-ovmf (AlmaLinux:8) 20210527gite1999b264f1f-3.el8; openssl (Alpine:v3.10) 1.1.1j-r0; openssl3 (Alpine:v3.15) 1.1.1j-r0.
- Mentioned 6 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Low priority for now. Upgrade to edk2-ovmf (AlmaLinux:8) 20210527gite1999b264f1f-3.el8; openssl (Alpine:v3.10) 1.1.1j-r0; openssl3 (Alpine:v3.15) 1.1.1j-r0 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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).
- BDU:2021-03744
- GHSA-84rm-qf37-fgc2
- ALSA-2021:4198
- DLA-2563-1
- DLA-2565-1
- DSA-4855-1
- openSUSE-SU-2021:0427-1
- openSUSE-SU-2021:0430-1
- RHSA-2021:3798
- RHSA-2021:4198
- RHSA-2021:4424
- RHSA-2021:4614
- RHSA-2021:4861
- RLSA-2021:4198
- RLSA-2021:4424
- RUSTSEC-2021-0058
- SUSE-SU-2021:0725-1
- SUSE-SU-2021:0752-1
- SUSE-SU-2021:0753-1
- SUSE-SU-2021:0754-1
- Published
- Feb 16, 2021
- Updated
- Jun 16, 2026
- EPSS
- 7.4% · 94th percentile
- CWE
- CWE-476
Report tools
Action score
25
Monitor
Low priority for now.
- CVSS
- 23 / 40 · 5.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 2 / 30 · 7.4%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- Proof of concept exists, no weaponized module
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| openssl | openssl | cpe:2.3:a:openssl:openssl |
| debian | debian linux | cpe:2.3:o:debian:debian_linux |
| tenable | nessus network monitor | cpe:2.3:a:tenable:nessus_network_monitor |
| tenable | tenable.sc | cpe:2.3:a:tenable:tenable.sc |
| apple | safari | cpe:2.3:a:apple:safari |
| apple | ipados | cpe:2.3:o:apple:ipados |
| apple | iphone os | cpe:2.3:o:apple:iphone_os |
| apple | macos | 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 | cpe:2.3:a:oracle:business_intelligence |
and 11 more
Check your server's TLS configuration
The OpenSSL version can't be seen from outside; the free SSL checker tests your certificate, enabled TLS versions and weak ciphers. Confirm the version on your server with the package manager.
Run the SSL checkAffected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- oracle mysql serverbefore 5.7.33
- oracle mysql server8.0.15 and later · before 8.0.23
Versions reported by the vendor
Affected version ranges reported by the assigning authority (openssl). Independent of NVD's CPE analysis and usually ahead of it.
OpenSSL OpenSSL
- 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)affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:8 | edk2-ovmf | before 20210527gite1999b264f1f-3.el8 | 20210527gite1999b264f1f-3.el8 |
| Alpine:v3.10 | openssl | from 1.0.2 · before 1.1.1j-r0 | 1.1.1j-r0 |
| Alpine:v3.15 | openssl3 | before 1.1.1j-r0 | 1.1.1j-r0 |
| Alpine:v3.17 | openssl1.1-compat | before 1.1.1j-r0 | 1.1.1j-r0 |
| crates.io | openssl-src | from 0.0.0-0 · before 111.14.0 | 111.14.0 |
| crates.io | openssl-src | before 111.14.0 | 111.14.0 |
| Debian:10 | openssl | before 1.1.1d-0+deb10u5 | 1.1.1d-0+deb10u5 |
| Debian:12 | openssl | before 1.1.1j-1 | 1.1.1j-1 |
| Debian:9 | openssl | before 1.1.0l-1~deb9u3 | 1.1.0l-1~deb9u3 |
| Debian:9 | openssl1.0 | before 1.0.2u-1~deb9u4 | 1.0.2u-1~deb9u4 |
| openSUSE:Leap 15.2 | openssl-1_0_0 | before 1.0.2p-lp152.8.12.1 | 1.0.2p-lp152.8.12.1 |
| openSUSE:Leap 15.2 | openssl-1_1 | before 1.1.1d-lp152.7.12.1 | 1.1.1d-lp152.7.12.1 |
| Red Hat:enterprise_linux:7::client | openssl | before 1:1.0.2k-22.el7_9 | 1:1.0.2k-22.el7_9 |
| Red Hat:enterprise_linux:7::client | openssl-debuginfo | before 1:1.0.2k-22.el7_9 | 1:1.0.2k-22.el7_9 |
| Red Hat:enterprise_linux:7::client | openssl-devel | before 1:1.0.2k-22.el7_9 | 1:1.0.2k-22.el7_9 |
| Red Hat:enterprise_linux:7::client | openssl-libs | before 1:1.0.2k-22.el7_9 | 1:1.0.2k-22.el7_9 |
| Red Hat:enterprise_linux:7::client | openssl-perl | before 1:1.0.2k-22.el7_9 | 1:1.0.2k-22.el7_9 |
| Red Hat:enterprise_linux:7::client | openssl-static | before 1:1.0.2k-22.el7_9 | 1:1.0.2k-22.el7_9 |
| Red Hat:enterprise_linux:8::appstream | edk2 | before 0:20210527gite1999b264f1f-3.el8 | 0:20210527gite1999b264f1f-3.el8 |
| Red Hat:enterprise_linux:8::appstream | edk2-aarch64 | before 0:20210527gite1999b264f1f-3.el8 | 0:20210527gite1999b264f1f-3.el8 |
| Red Hat:enterprise_linux:8::appstream | edk2-ovmf | before 0:20210527gite1999b264f1f-3.el8 | 0:20210527gite1999b264f1f-3.el8 |
| Red Hat:enterprise_linux:8::baseos | openssl | before 1:1.1.1k-4.el8 | 1:1.1.1k-4.el8 |
| Red Hat:enterprise_linux:8::baseos | openssl-debuginfo | before 1:1.1.1k-4.el8 | 1:1.1.1k-4.el8 |
| Red Hat:enterprise_linux:8::baseos | openssl-debugsource | before 1:1.1.1k-4.el8 | 1:1.1.1k-4.el8 |
+96
Same product
openssl: all recordsOther highest-scoring records for the same primary product.
- CVE-2014-0160The (1) TLS and (2) DTLS implementations in OpenSSL 1.0.1 before 1.0.1g do not properly handle Heartbeat Extension packets, which allows remKEV90Now
- CVE-2021-3711SM2 Decryption Buffer Overflow65This week
- CVE-2003-0545Double free vulnerability in OpenSSL 0.9.7 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code 65This week
Published before and after this one in the same product
- ← EarlierCVE-2021-23839Feb 16, 2021 · Incorrect SSLv2 rollback protection15Monitor
- ← EarlierCVE-2021-23840Feb 16, 2021 · Integer overflow in CipherUpdate45Plan
- Later →CVE-2021-3449Mar 25, 2021 · NULL pointer deref in signature_algorithms processing42Plan
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| almalinux:edk2-ovmf | 20210527gite1999b264f1f-3.el8 · AlmaLinux:8 | Package registry (OSV) |
| alpine:openssl | 1.1.1j-r0 · Alpine:v3.10 | Package registry (OSV) |
| alpine:openssl1.1-compat | 1.1.1j-r0 · Alpine:v3.17 | Package registry (OSV) |
| alpine:openssl3 | 1.1.1j-r0 · Alpine:v3.15 | Package registry (OSV) |
| crates.io:openssl-src | 111.14.0 | Package registry (OSV) |
| debian:openssl | 1.1.1j-1 · Debian:12 | Package registry (OSV) |
| debian:openssl1.0 | 1.0.2u-1~deb9u4 · Debian:9 | Package registry (OSV) |
| opensuse:openssl-1_0_0 | 1.0.2p-lp152.8.12.1 · openSUSE:Leap 15.2 | Package registry (OSV) |
| opensuse:openssl-1_1 | 1.1.1d-lp152.7.12.1 · openSUSE:Leap 15.2 | Package registry (OSV) |
| red hat:edk2 | 0:20210527gite1999b264f1f-3.el8 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:edk2-aarch64 | 0:20210527gite1999b264f1f-3.el8 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:edk2-ovmf | 0:20210527gite1999b264f1f-3.el8 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:jbcs-httpd24-apr | 0:1.6.3-107.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:openssl | 1:1.0.2k-22.el7_9 · Red Hat:enterprise_linux:7::client | Package registry (OSV) |
| red hat:openssl-debuginfo | 1:1.0.2k-22.el7_9 · Red Hat:enterprise_linux:7::client | Package registry (OSV) |
| red hat:openssl-debugsource | 1:1.1.1k-4.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:openssl-devel | 1:1.0.2k-22.el7_9 · Red Hat:enterprise_linux:7::client | Package registry (OSV) |
| red hat:openssl-libs | 1:1.0.2k-22.el7_9 · Red Hat:enterprise_linux:7::client | Package registry (OSV) |
| red hat:openssl-libs-debuginfo | 1:1.1.1k-4.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:openssl-perl | 1:1.0.2k-22.el7_9 · Red Hat:enterprise_linux:7::client | Package registry (OSV) |
| red hat:openssl-static | 1:1.0.2k-22.el7_9 · Red Hat:enterprise_linux:7::client | Package registry (OSV) |
| rocky linux:edk2 | 0:20210527gite1999b264f1f-3.el8 · Rocky Linux:8 | Package registry (OSV) |
| rocky linux:openssl | 1:1.1.1k-4.el8 · Rocky Linux:8 | Package registry (OSV) |
| suse:compat-openssl098 | 0.9.8j-106.24.1 · SUSE:Linux Enterprise Module for Legacy 12 | Package registry (OSV) |
| suse:openssl | 1.0.2j-60.66.1 · SUSE:HPE Helion OpenStack 8 | Package registry (OSV) |
| suse:openssl-1_0_0 | 1.0.2p-3.36.1 · SUSE:OpenStack Cloud 9 | Package registry (OSV) |
| suse:openssl-1_1 | 1.1.1d-2.30.1 · SUSE:OpenStack Cloud 9 | Package registry (OSV) |
| suse:openssl1 | 1.0.1g-0.58.33.1 · SUSE:Linux Enterprise Server 11-SECURITY | Package registry (OSV) |
Exploit status
Proof of concept available
A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.
Evidence
- Proof-of-concept repository on GitHub ×2
Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.
| Source | Kind | Date |
|---|---|---|
| Proof-of-concept repository on GitHub | stars:0 | 2022-04-29 |
| Proof-of-concept repository on GitHub | stars:0 | 2022-08-05 |
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- Published
- First PoC+436 d
- TodayNov 9, 2026+2092 d
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-22-0222 · Mar 15, 2022(RedHat Güvenlik Güncellemesi)
- TR-22-0016 · Jan 7, 2022(IBM Güvenlik Zafiyeti)
- TR-21-0964 · Dec 3, 2021(Hitachi Güvenlik Zafiyeti)
- TR-21-0963 · Dec 2, 2021(RedHat Güvenlik Güncellemesi)
- TR-21-0911 · Nov 10, 2021(RedHat Güvenlik Güncellemesi)
- TR-21-0756 · Sep 20, 2021(IBM Güvenlik Bülteni Yayınladı)
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- none
- Integrity
- none
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- High
Weakness class (CWE)
CWE-476 · NULL Pointer DereferenceCVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (19 more)Show less
- seclists.org/fulldisclosure/2021/May/68
- seclists.org/fulldisclosure/2021/May/70
- cert-portal.siemens.com/productcert/pdf/ssa-637483.pdf
- git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=122a19ab48091c657f7cb1fb3af9fc07bd557bbf
- git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=8252ee4d90f3f2004d3d0aeeed003ad49c9a7807
- kb.pulsesecure.net/articles/Pulse_Security_Advisories/SA44846
- security.gentoo.org/glsa/202103-03
- security.netapp.com/advisory/ntap-20210219-0009/
- security.netapp.com/advisory/ntap-20210513-0002/
- security.netapp.com/advisory/ntap-20240621-0006/
- support.apple.com/kb/HT212528
- support.apple.com/kb/HT212529
- support.apple.com/kb/HT212534
- www.debian.org/security/2021/dsa-4855
- www.openssl.org/news/secadv/20210216.txt
- www.oracle.com//security-alerts/cpujul2021.html
- www.oracle.com/security-alerts/cpuApr2021.html
- www.oracle.com/security-alerts/cpuapr2022.html
- www.oracle.com/security-alerts/cpuoct2021.html
Vendor advisories and official records. Exploit/PoC links are deliberately left out.