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Full vulnerability report · 2021
CVE-2021-20232High confidence

A flaw was found in gnutls

n/a · gnutls

9.8CriticalCVSS 3.1
Recommended action
Within 72 hours

Critical technical impact with a remotely reachable, unauthenticated path; no CISA KEV confirmation is currently recorded.

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 flaw was found in gnutls. A use after free issue in client_send_params in lib/ext/pre_shared_key.c may lead to memory corruption and other potential consequences.
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-2021-7671

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 actionWithin 72 hours

Critical technical impact with a remotely reachable, unauthenticated path; no CISA KEV confirmation is currently recorded.

Patch available
01

What, why and how

A flaw was found in gnutls. A use after free issue in client_send_params in lib/ext/pre_shared_key.c may lead to memory corruption and other potential consequences.

What

A flaw was found in gnutls. A use after free issue in client_send_params in lib/ext/pre_shared_key.c may lead to memory corruption and other potential consequences.

Why

The program can continue using memory after it has been released, producing unsafe and attacker-influenceable behaviour.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

A flaw was found in gnutls. A use after free issue in client_send_params in lib/ext/pre_shared_key.c may lead to memory corruption and other potential consequences.

Why

The program can continue using memory after it has been released, producing unsafe and attacker-influenceable behaviour.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

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 → Use After Free → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
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-416 ↗

CWE-416: Use After Free. The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

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:L/PR:N/UI:N/S:U/C:H/I:H/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.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.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.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.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.
NetworkUnauthenticatedCWE-416
A

Official authority intelligence

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

BSI · German · WID-SEC-W-2026-3127GnuTLS: Mehrere Schwachstellen

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in GnuTLS ausnutzen, um beliebigen Programmcode auszuführen oder einen Denial of Service State herbeizuführen.

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

rg/CVERecord?id=CVE-2020-8284 Référence CVE CVE-2020-8285 https://www.cve.org/CVERecord?id=CVE-2020-8285 Référence CVE CVE-2020-8286 https://www.cve.org/CVERecord?id=CVE-2020-8286 Référence CVE CVE-2020-8315 https://www.cve.org/CVERecord?id=CVE-2020-8315 Référence CVE CVE-2020-8492 https://www.cve.org/CVERecord?id=CVE-2020-8492 Référence CVE CVE-2020-9327 https://www.cve.org/CVERecord?id=CVE-2020-9327 Référence CVE CVE-2021-20193 https://www.cve.org/CVERecord?id=CVE-2021-20193 Référence CVE CVE-2021-20227 https://www.cve.org/CVERecord?id=CVE-2021-20227 Référence CVE CVE-2021-20231 https://www.cve.org/CVERecord?id=CVE-2021-20231 Référence CVE CVE-2021-20232 https://www.cve.org/CVERecord?id=CVE-2021-20232 Référence CVE CVE-2021-20305 https://www.cve.org/CVERecord?id=CVE-2021-20305 Référence CVE CVE-2021-22876 https://www.cve.org/CVERecord?id=CVE-2021-22876 Référence CVE CVE-2021-22890 https://www.cve.org/CVERecord?id=CVE-2021-22890 Référence CVE CVE-2021-22897 https://www.cve.org/CVERecord?id=CVE-2021-22897 Référence CVE CVE-2021-22898 https://www.cve.org/CVERecord?id=CVE-2021-22898 Référence CVE CVE-2021-22901 https://www.cve.org/CVERecord?id=CVE-2021-22901 Référence CVE CVE-2021-22922 https://www.cve.org/CVERecord?id=CVE-2021-22922 Référence CVE CVE-2021-22923 https://www.cve.org/CVERecord?id=

Official advisory
CERT-FR · French · CERTFR-2022-AVI-386Multiples vulnérabilités dans IBM QRadar SIEM

ecord?id=CVE-2019-17595 Référence CVE CVE-2019-20838 https://www.cve.org/CVERecord?id=CVE-2019-20838 Référence CVE CVE-2020-12762 https://www.cve.org/CVERecord?id=CVE-2020-12762 Référence CVE CVE-2020-14155 https://www.cve.org/CVERecord?id=CVE-2020-14155 Référence CVE CVE-2020-16135 https://www.cve.org/CVERecord?id=CVE-2020-16135 Référence CVE CVE-2020-24370 https://www.cve.org/CVERecord?id=CVE-2020-24370 Référence CVE CVE-2020-8022 https://www.cve.org/CVERecord?id=CVE-2020-8022 Référence CVE CVE-2020-9488 https://www.cve.org/CVERecord?id=CVE-2020-9488 Référence CVE CVE-2021-20231 https://www.cve.org/CVERecord?id=CVE-2021-20231 Référence CVE CVE-2021-20232 https://www.cve.org/CVERecord?id=CVE-2021-20232 Référence CVE CVE-2021-20266 https://www.cve.org/CVERecord?id=CVE-2021-20266 Référence CVE CVE-2021-22096 https://www.cve.org/CVERecord?id=CVE-2021-22096 Référence CVE CVE-2021-22876 https://www.cve.org/CVERecord?id=CVE-2021-22876 Référence CVE CVE-2021-22898 https://www.cve.org/CVERecord?id=CVE-2021-22898 Référence CVE CVE-2021-22925 https://www.cve.org/CVERecord?id=CVE-2021-22925 Référence CVE CVE-2021-22946 https://www.cve.org/CVERecord?id=CVE-2021-22946 Référence CVE CVE-2021-23214 https://www.cve.org/CVERecord?id=CVE-2021-23214 Référence CVE CVE-2021-2369 https://www.cve.org/CVERecord?id=C

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 12 Mar 2021 · Last source change 3 Dec 2025, 15:03 UTC · CWE-416 · Use After Free

CVE recordCVE.org · 5.2
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-2021-7671
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-2021-7671↗Vendor CSAF · Siemens ProductCERT↗CVE authority or vendor reference↗Patch or update 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-2021-20232 · cve.blacktree.nl