BlackTreeIndependent security intelligence
← Back to the CVE catalogue
Full vulnerability report · 2021
CVE-2021-3537High confidence

A vulnerability found in libxml2 in versions before 2.9.11 shows that it did not propagate errors while parsing XML mixed content, causing a NULL dereference

n/a · libxml2

5.9MediumCVSS 3.1
Recommended action
Scheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
Direct vendor intelligence

Authoritative 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.

1 current
SSA-398330 · CSAF 2.0 · revision 18 · interimSiemens ProductCERTSSA-398330: Vulnerabilities in the additional GNU/Linux subsystem of the SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP >= V3.1.0 and < V3.1.5
5 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)
  • SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0)
  • SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0)
  • SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0)
  • SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0)
Summary
A vulnerability found in libxml2 in versions before 2.9.11 shows that it did not propagate errors while parsing XML mixed content, causing a NULL dereference. If an untrusted XML document was parsed in recovery mode and post-validated, the flaw could be used to crash the application. The highest threat from this vulnerability is to system availability.
Remediation
Update to V3.1.5 or later version
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2022-1938

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
01

What, why and how

A vulnerability found in libxml2 in versions before 2.9.11 shows that it did not propagate errors while parsing XML mixed content, causing a NULL dereference. If an untrusted XML document was parsed in recovery mode and post-validated, the flaw could be used to crash the application. The highest threat from this vulnerability is to system availability.

What

A vulnerability found in libxml2 in versions before 2.9.11 shows that it did not propagate errors while parsing XML mixed content, causing a NULL dereference. If an untrusted XML document was parsed in recovery mode and post-validated, the flaw could be used to crash the application. The highest threat from this vulnerability is to system availability.

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

A vulnerability found in libxml2 in versions before 2.9.11 shows that it did not propagate errors while parsing XML mixed content, causing a NULL dereference. If an untrusted XML document was parsed in recovery mode and post-validated, the flaw could be used to crash the application. The highest threat from this vulnerability is to system availability.

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
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

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
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

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:H

Common 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.
NetworkUnauthenticatedDenial of serviceCWE-476
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-W-2023-1614Tenable Security Nessus Network Monitor: Mehrere Schwachstellen

Ein entfernter, anonymer, authentisierter oder lokaler Angreifer kann mehrere Schwachstellen in Tenable Security Nessus Network Monitor ausnutzen, um beliebigen Code auszuführen, vertrauliche Informationen offenzulegen, einen Denial-of-Service-Zustand auszulösen und Daten zu manipulieren.

Official advisory
BSI · German · WID-SEC-W-2023-0395Splunk Splunk Enterprise: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Splunk Splunk Enterprise ausnutzen, um vertrauliche Informationen offenzulegen, Sicherheitsmaßnahmen zu umgehen, einen Denial-of-Service-Zustand zu verursachen, Daten zu manipulieren und einen Cross-Site-Scripting-Angriff durchzuführen.

Official advisory
BSI · German · WID-SEC-W-2023-1151libxml2: Schwachstelle ermöglicht Denial of Service

Ein entfernter, anonymer Angreifer kann eine Schwachstelle in libxml2 ausnutzen, um einen Denial of Service Angriff durchzuführen.

Official advisory
CERT-FR · French · CERTFR-2023-AVI-1015Multiples vulnérabilités dans les produits Siemens

g/CVERecord?id=CVE-2021-33294 Référence CVE CVE-2021-33560 https://www.cve.org/CVERecord?id=CVE-2021-33560 Référence CVE CVE-2021-33574 https://www.cve.org/CVERecord?id=CVE-2021-33574 Référence CVE CVE-2021-33910 https://www.cve.org/CVERecord?id=CVE-2021-33910 Référence CVE CVE-2021-3426 https://www.cve.org/CVERecord?id=CVE-2021-3426 Référence CVE CVE-2021-3516 https://www.cve.org/CVERecord?id=CVE-2021-3516 Référence CVE CVE-2021-3517 https://www.cve.org/CVERecord?id=CVE-2021-3517 Référence CVE CVE-2021-3518 https://www.cve.org/CVERecord?id=CVE-2021-3518 Référence CVE CVE-2021-3520 https://www.cve.org/CVERecord?id=CVE-2021-3520 Référence CVE CVE-2021-3537 https://www.cve.org/CVERecord?id=CVE-2021-3537 Référence CVE CVE-2021-3541 https://www.cve.org/CVERecord?id=CVE-2021-3541 Référence CVE CVE-2021-3580 https://www.cve.org/CVERecord?id=CVE-2021-3580 Référence CVE CVE-2021-35942 https://www.cve.org/CVERecord?id=CVE-2021-35942 Référence CVE CVE-2021-36084 https://www.cve.org/CVERecord?id=CVE-2021-36084 Référence CVE CVE-2021-36085 https://www.cve.org/CVERecord?id=CVE-2021-36085 Référence CVE CVE-2021-36086 https://www.cve.org/CVERecord?id=CVE-2021-36086 Référence CVE CVE-2021-36087 https://www.cve.org/CVERecord?id=CVE-2021-36087 Référence CVE CVE-2021-36222 https://www.cve.org/CVERecord?id=CVE-2

Official advisory
CERT-FR · French · CERTFR-2023-AVI-0499Multiples vulnérabilités dans Tenable Nessus Network Monitor

CVERecord?id=CVE-2020-35525 Référence CVE CVE-2020-35527 https://www.cve.org/CVERecord?id=CVE-2020-35527 Référence CVE CVE-2020-7595 https://www.cve.org/CVERecord?id=CVE-2020-7595 Référence CVE CVE-2020-9327 https://www.cve.org/CVERecord?id=CVE-2020-9327 Référence CVE CVE-2021-20227 https://www.cve.org/CVERecord?id=CVE-2021-20227 Référence CVE CVE-2021-30560 https://www.cve.org/CVERecord?id=CVE-2021-30560 Référence CVE CVE-2021-31239 https://www.cve.org/CVERecord?id=CVE-2021-31239 Référence CVE CVE-2021-3517 https://www.cve.org/CVERecord?id=CVE-2021-3517 Référence CVE CVE-2021-3518 https://www.cve.org/CVERecord?id=CVE-2021-3518 Référence CVE CVE-2021-3537 https://www.cve.org/CVERecord?id=CVE-2021-3537 Référence CVE CVE-2021-3541 https://www.cve.org/CVERecord?id=CVE-2021-3541 Référence CVE CVE-2021-36690 https://www.cve.org/CVERecord?id=CVE-2021-36690 Référence CVE CVE-2021-3672 https://www.cve.org/CVERecord?id=CVE-2021-3672 Référence CVE CVE-2021-45346 https://www.cve.org/CVERecord?id=CVE-2021-45346 Référence CVE CVE-2022-22576 https://www.cve.org/CVERecord?id=CVE-2022-22576 Référence CVE CVE-2022-23308 https://www.cve.org/CVERecord?id=CVE-2022-23308 Référence CVE CVE-2022-23395 https://www.cve.org/CVERecord?id=CVE-2022-23395 Référence CVE CVE-2022-27774 https://www.cve.org/CVERecord?id=CVE-2

Official advisory
CERT-FR · French · CERTFR-2023-AVI-0142Multiples vulnérabilités dans les produits Splunk

m/advisories/SVD-2023-0205 Bulletin de sécurité Splunk SVD-2023-0210 du 14 février 2023 https://advisory.splunk.com/advisories/SVD-2023-0210 Bulletin de sécurité Splunk SVD-2023-0215 du 14 février 2023 https://advisory.splunk.com/advisories/SVD-2023-0215 Référence CVE CVE-2015-20107 https://www.cve.org/CVERecord?id=CVE-2015-20107 Référence CVE CVE-2021-21419 https://www.cve.org/CVERecord?id=CVE-2021-21419 Référence CVE CVE-2021-28957 https://www.cve.org/CVERecord?id=CVE-2021-28957 Référence CVE CVE-2021-3517 https://www.cve.org/CVERecord?id=CVE-2021-3517 Référence CVE CVE-2021-3518 https://www.cve.org/CVERecord?id=CVE-2021-3518 Référence CVE CVE-2021-3537 https://www.cve.org/CVERecord?id=CVE-2021-3537 Référence CVE CVE-2022-24785 https://www.cve.org/CVERecord?id=CVE-2022-24785 Référence CVE CVE-2022-31129 https://www.cve.org/CVERecord?id=CVE-2022-31129 Référence CVE CVE-2022-32212 https://www.cve.org/CVERecord?id=CVE-2022-32212 Référence CVE CVE-2023-22931 https://www.cve.org/CVERecord?id=CVE-2023-22931 Référence CVE CVE-2023-22932 https://www.cve.org/CVERecord?id=CVE-2023-22932 Référence CVE CVE-2023-22933 https://www.cve.org/CVERecord?id=CVE-2023-22933 Référence CVE CVE-2023-22934 https://www.cve.org/CVERecord?id=CVE-2023-22934 Référence CVE CVE-2023-22935 https://www.cve.org/CVERecord?id=C

Official advisory
CERT-FR · French · CERTFR-2021-AVI-791Multiples vulnérabilités dans les produits IBM

ve.org/CVERecord?id=CVE-2021-3326 Référence CVE CVE-2021-33910 https://www.cve.org/CVERecord?id=CVE-2021-33910 Référence CVE CVE-2021-3421 https://www.cve.org/CVERecord?id=CVE-2021-3421 Référence CVE CVE-2021-3449 https://www.cve.org/CVERecord?id=CVE-2021-3449 Référence CVE CVE-2021-3450 https://www.cve.org/CVERecord?id=CVE-2021-3450 Référence CVE CVE-2021-3516 https://www.cve.org/CVERecord?id=CVE-2021-3516 Référence CVE CVE-2021-3517 https://www.cve.org/CVERecord?id=CVE-2021-3517 Référence CVE CVE-2021-3518 https://www.cve.org/CVERecord?id=CVE-2021-3518 Référence CVE CVE-2021-3520 https://www.cve.org/CVERecord?id=CVE-2021-3520 Référence CVE CVE-2021-3537 https://www.cve.org/CVERecord?id=CVE-2021-3537 Référence CVE CVE-2021-3541 https://www.cve.org/CVERecord?id=CVE-2021-3541 Référence CVE CVE-2021-3609 https://www.cve.org/CVERecord?id=CVE-2021-3609 Gestion détaillée du document le 15 octobre 2021 Version initiale Alertes Avis Bulletins d’actualités Mentions légales Conditions générales À propos Contact cyber.gouv.fr service-public.fr legifrance.gouv.fr info.gouv.fr france.fr info.gouv.fr/risques Premier Ministre / Secrétariat Général de la Défense et de la Sécurité Nationale / Agence nationale de la sécurité des systèmes d'information

Official advisory
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.
Patch available
Affected
SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0); SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0); SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0); SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0); SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0)
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.
Action
Update to V3.1.5 or later version
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 14 May 2021 · Last source change 3 Aug 2024, 17:01 UTC · CWE-476 · NULL Pointer Dereference

CVE recordCVE.org · 5.1
CVSS sourceNIST NVD
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2022-1938
Product sourceVendor CSAF · Siemens ProductCERT
Remediation sourceVendor CSAF · Siemens ProductCERT
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2022-1938↗Vendor CSAF · Siemens ProductCERT↗Patch or update reference↗Patch or update reference↗Patch or update reference↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
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.
Free version - for non-commercial use only.CVE-2021-3537 · cve.blacktree.nl