Evidence used
- No CISA KEV confirmation is currently recorded.
- The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
- EPSS is 7.41% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2021
CVE-2021-23841High confidence
Null pointer deref in X509_issuer_and_serial_hash()
OpenSSL · OpenSSL
5.9MediumCVSS 3.1
Patch only the product branches with a verified fix
Fix availability varies by productMedium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityMedium→Operational priority:Medium, unchanged from published severity.unchanged
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs OpenSSL OpenSSL and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Remediation availability differs by product scope
Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
- Siemens ProductCERT: 1 affected or under-investigation product state without a fixed product state in the same current advisory
Distribution package intelligence
7 package statesRelease-specific package status
Alpine, Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
| Distribution release | Source package | Vendor state | Fixed version | Evidence |
|---|---|---|---|---|
| Alpine v3.23v3.23 · main | openssl | Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected. | 1.1.1j-r0 | Alpine Security Database ↗Source updated 3 Oct 2026 |
| Alpine v3.22v3.22 · main | openssl | Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected. | 1.1.1j-r0 | Alpine Security Database ↗Source updated 3 Oct 2026 |
| Alpine v3.21v3.21 · main | openssl | Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected. | 1.1.1j-r0 | Alpine Security Database ↗Source updated 3 Oct 2026 |
| Debian trixietrixie · source | openssl | Vendor fix publishedDebian records a fixed source-package version for this release. | 1.1.1j-1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian bookwormbookworm · source | openssl | Vendor fix publishedDebian records a fixed source-package version for this release. | 1.1.1j-1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian forkyforky · source | openssl | Vendor fix publishedDebian records a fixed source-package version for this release. | 1.1.1j-1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian sidsid · source | openssl | Vendor fix publishedDebian records a fixed source-package version for this release. | 1.1.1j-1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
Direct vendor intelligence
2 currentAuthoritative vendor CSAF and VEX advisories
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
CVE-2021-23841 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityopenssl: NULL pointer dereference in X509_issuer_and_serial_hash()
The vendor explicitly identifies these products as affected by this CVE.
- management-ingress.src as a component of Red Hat Advanced Cluster Management for Kubernetes 2
- openssl as a component of Red Hat Enterprise Linux 6
- openssl-devel as a component of Red Hat Enterprise Linux 6
- openssl-perl as a component of Red Hat Enterprise Linux 6
- openssl-static as a component of Red Hat Enterprise Linux 6
- openssl.src as a component of Red Hat Enterprise Linux 6
- openssl098e as a component of Red Hat Enterprise Linux 6
- openssl098e.src as a component of Red Hat Enterprise Linux 6
- AAVMF as a component of Red Hat Enterprise Linux 7
- OVMF as a component of Red Hat Enterprise Linux 7
- openssl098e as a component of Red Hat Enterprise Linux 7
- openssl098e.src as a component of Red Hat Enterprise Linux 7
- Summary
- 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.
- Remediation
- For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 For the update to take effect, all services linked to the OpenSSL library must be restarted, or the system rebooted.
SSA-637483 · CSAF 2.0 · revision 1 · finalSiemens ProductCERTSSA-637483 Third-Party Component Vulnerabilities in SINEC INS before V1.0 SP2
The vendor explicitly identifies these products as affected by this CVE.
- SINEC INS
- Summary
- 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).
- Remediation
- Update to V1.0 SP2 or later version
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Fix availability varies by product01
What, why and how
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).
What
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).
Why
The product dereferences a pointer that it expects to be valid but is NULL.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
What
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).
Why
The product dereferences a pointer that it expects to be valid but is NULL.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
- Likely attack path
- a network path → NULL Pointer Dereference → disrupt the affected service
- Attack surface
- Network
- Privileges required
- None: unauthenticated exploitation is possible
- User interaction
- None
- Attack complexity
- High: exploitation depends on specific conditions
- Security boundary
- Unchanged: impact remains within the vulnerable component's security authority
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-476 ↗
CWE-476: NULL Pointer Dereference. The product dereferences a pointer that it expects to be valid but is NULL.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:HCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.- Post-exploitation / living off the land
- No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
03
Patch and workaround
Operational remediation based on structured source evidence.
- Status
?
Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change. - Fix availability varies by product
- Affected
- management-ingress.src as a component of Red Hat Advanced Cluster Management for Kubernetes 2
- openssl as a component of Red Hat Enterprise Linux 6
- openssl-devel as a component of Red Hat Enterprise Linux 6
- openssl-perl as a component of Red Hat Enterprise Linux 6
- openssl-static as a component of Red Hat Enterprise Linux 6
- openssl.src as a component of Red Hat Enterprise Linux 6
- openssl098e as a component of Red Hat Enterprise Linux 6
- openssl098e.src as a component of Red Hat Enterprise Linux 6
- AAVMF as a component of Red Hat Enterprise Linux 7
- OVMF as a component of Red Hat Enterprise Linux 7
- openssl098e as a component of Red Hat Enterprise Linux 7
- openssl098e.src as a component of Red Hat Enterprise Linux 7
- ovmf.src as a component of Red Hat Enterprise Linux 7
- compat-openssl10 as a component of Red Hat Enterprise Linux 8
- compat-openssl10.src as a component of Red Hat Enterprise Linux 8
- openssl.src as a component of Red Hat JBoss Enterprise Application Platform 6
- Fixed
- openssl-1:1.0.2k-22.el7_9.src as a component of Red Hat Enterprise Linux Client (v. 7)
- openssl-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux Client (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux Client (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux Client (v. 7)
- openssl-libs-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux Client (v. 7)
- openssl-libs-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux Client (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux Client Optional (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux Client Optional (v. 7)
- openssl-devel-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux Client Optional (v. 7)
- openssl-devel-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux Client Optional (v. 7)
- openssl-perl-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux Client Optional (v. 7)
- openssl-static-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux Client Optional (v. 7)
- openssl-static-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux Client Optional (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux ComputeNode Optional (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux ComputeNode Optional (v. 7)
- openssl-devel-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux ComputeNode Optional (v. 7)
- openssl-devel-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux ComputeNode Optional (v. 7)
- openssl-perl-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux ComputeNode Optional (v. 7)
- openssl-static-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux ComputeNode Optional (v. 7)
- openssl-static-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux ComputeNode Optional (v. 7)
- openssl-1:1.0.2k-22.el7_9.ppc64 as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-1:1.0.2k-22.el7_9.ppc64le as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-1:1.0.2k-22.el7_9.s390x as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-1:1.0.2k-22.el7_9.src as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-1:1.0.2k-22.el7_9.x86_64 as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.i686 as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.ppc as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.ppc64 as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.ppc64le as a component of Red Hat Enterprise Linux Server (v. 7)
- openssl-debuginfo-1:1.0.2k-22.el7_9.s390 as a component of Red Hat Enterprise Linux Server (v. 7)
- and 264 more
- Action
- Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
- Workaround
- No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 16 Feb 2021 · Last source change 16 Sept 2024, 22:39 UTC · CWE-476 · NULL Pointer Dereference
CVE recordCVE.org · 5.1
CVSS sourceNIST NVD
EPSS source FIRST · tracked since 2026-08-14
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2021-1630
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceNIST NVD
NVD statusNVD modified after enrichment
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
- Affected versionsThe structured affected or fixed version information changed.Red Hat Product Security ↗
- Before
- 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) · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- After
- 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) · Fixed: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 For the update to take effect, all services linked to the OpenSSL library must be restarted, or the system rebooted.
CVE published
Fixed release or patch reference recorded
Fixed release recorded from official guidance
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.