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Full vulnerability report · 2021
CVE-2021-28363High confidence

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies

Unknown · Unknown

Official source articles: Siemens SSA-398330 ↗ · GitHub GHSA-5PHF-PP7P-VC2R ↗. Check the applicable product and release in the original source.

6.5MediumCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

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 5 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Medium, unchanged from published severity.unchanged

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 2.11% for the current model date.

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

  1. Confirm that the asset runs Unknown Unknown and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 5 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-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.

7 package states
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 releaseSource packageVendor stateFixed versionEvidence
Alpine v3.23v3.23 · mainpy3-urllib3Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.1.26.4-r0Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.22v3.22 · mainpy3-urllib3Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.1.26.4-r0Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.21v3.21 · mainpy3-urllib3Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.1.26.4-r0Alpine Security Database ↗Source updated 3 Oct 2026
Debian trixietrixie · sourcepython-urllib3Vendor fix publishedDebian records a fixed source-package version for this release.1.26.4-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcepython-urllib3Vendor fix publishedDebian records a fixed source-package version for this release.1.26.4-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcepython-urllib3Vendor fix publishedDebian records a fixed source-package version for this release.1.26.4-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcepython-urllib3Vendor fix publishedDebian records a fixed source-package version for this release.1.26.4-1Debian Security Tracker ↗Source updated 6 Oct 2026
Open-source package ranges1 source-attributed range

These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.

Ecosystem and packageAffected rangeFirst fixed versionEvidence
pipurllib3>= 1.26.0, < 1.26.41.26.4GitHub advisory ↗upstream repository advisory · 18 Nov 2024
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
The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.
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.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

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-2021-0457

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 actionPatch only the product branches with a verified fix

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 5 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.

What

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.

Why

The product does not validate, or incorrectly validates, a certificate.

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

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.

Why

The product does not validate, or incorrectly validates, a certificate.

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 → Improper Certificate Validation → 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-295 ↗

CWE-295: Improper Certificate Validation. The product does not validate, or incorrectly validates, a certificate.

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:L/I:L/A:N

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.CLowConfidentiality impact: A successful attack can cause a limited loss.ILowIntegrity impact: A successful attack can cause a limited loss.ANoneAvailability impact: No direct loss is represented by this metric.
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-295
A

Official authority intelligence

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

Cyber Security Agency of Singapore · English · CSA-SB-20210317Security Bulletin 17 Mar 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 17 Mar 2021, published on 17 March 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0366Multiples vulnérabilités dans les produits IBM

-2016-10516 Référence CVE CVE-2016-10745 https://www.cve.org/CVERecord?id=CVE-2016-10745 Référence CVE CVE-2018-1000656 https://www.cve.org/CVERecord?id=CVE-2018-1000656 Référence CVE CVE-2018-18074 https://www.cve.org/CVERecord?id=CVE-2018-18074 Référence CVE CVE-2019-1010083 https://www.cve.org/CVERecord?id=CVE-2019-1010083 Référence CVE CVE-2019-14322 https://www.cve.org/CVERecord?id=CVE-2019-14322 Référence CVE CVE-2020-15366 https://www.cve.org/CVERecord?id=CVE-2020-15366 Référence CVE CVE-2020-25032 https://www.cve.org/CVERecord?id=CVE-2020-25032 Référence CVE CVE-2020-28493 https://www.cve.org/CVERecord?id=CVE-2020-28493 Référence CVE CVE-2021-28363 https://www.cve.org/CVERecord?id=CVE-2021-28363 Référence CVE CVE-2021-30465 https://www.cve.org/CVERecord?id=CVE-2021-30465 Référence CVE CVE-2021-43565 https://www.cve.org/CVERecord?id=CVE-2021-43565 Référence CVE CVE-2021-43784 https://www.cve.org/CVERecord?id=CVE-2021-43784 Référence CVE CVE-2021-45958 https://www.cve.org/CVERecord?id=CVE-2021-45958 Référence CVE CVE-2022-23539 https://www.cve.org/CVERecord?id=CVE-2022-23539 Référence CVE CVE-2022-23540 https://www.cve.org/CVERecord?id=CVE-2022-23540 Référence CVE CVE-2022-23541 https://www.cve.org/CVERecord?id=CVE-2022-23541 Référence CVE CVE-2022-29162 https://www.cve.org/CVERecord?id=

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

d?id=CVE-2021-22946 Référence CVE CVE-2021-22947 https://www.cve.org/CVERecord?id=CVE-2021-22947 Référence CVE CVE-2021-23336 https://www.cve.org/CVERecord?id=CVE-2021-23336 Référence CVE CVE-2021-27212 https://www.cve.org/CVERecord?id=CVE-2021-27212 Référence CVE CVE-2021-27218 https://www.cve.org/CVERecord?id=CVE-2021-27218 Référence CVE CVE-2021-27219 https://www.cve.org/CVERecord?id=CVE-2021-27219 Référence CVE CVE-2021-27645 https://www.cve.org/CVERecord?id=CVE-2021-27645 Référence CVE CVE-2021-28041 https://www.cve.org/CVERecord?id=CVE-2021-28041 Référence CVE CVE-2021-28153 https://www.cve.org/CVERecord?id=CVE-2021-28153 Référence CVE CVE-2021-28363 https://www.cve.org/CVERecord?id=CVE-2021-28363 Référence CVE CVE-2021-28861 https://www.cve.org/CVERecord?id=CVE-2021-28861 Référence CVE CVE-2021-31239 https://www.cve.org/CVERecord?id=CVE-2021-31239 Référence CVE CVE-2021-3177 https://www.cve.org/CVERecord?id=CVE-2021-3177 Référence CVE CVE-2021-32292 https://www.cve.org/CVERecord?id=CVE-2021-32292 Référence CVE CVE-2021-3326 https://www.cve.org/CVERecord?id=CVE-2021-3326 Référence CVE CVE-2021-33294 https://www.cve.org/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-

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-804Multiples vulnérabilités dans Oracle PeopleSoft

De multiples vulnérabilités ont été découvertes dans Oracle PeopleSoft. Elles permettent à un attaquant de provoquer un déni de service à distance, une atteinte à l'intégrité des données et une atteinte à la confidentialité des données.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-505Multiples vulnérabilités dans IBM Spectrum

De multiples vulnérabilités ont été découvertes dans IBM Spectrum. Elles permettent à un attaquant de provoquer une exécution de code arbitraire à distance, une atteinte à l'intégrité des données et une atteinte à la confidentialité des données.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-490Multiples vulnérabilités dans IBM Spectrum Protect

d?id=CVE-2021-21348 Référence CVE CVE-2021-21349 https://www.cve.org/CVERecord?id=CVE-2021-21349 Référence CVE CVE-2021-21350 https://www.cve.org/CVERecord?id=CVE-2021-21350 Référence CVE CVE-2021-21351 https://www.cve.org/CVERecord?id=CVE-2021-21351 Référence CVE CVE-2021-21362 https://www.cve.org/CVERecord?id=CVE-2021-21362 Référence CVE CVE-2021-22883 https://www.cve.org/CVERecord?id=CVE-2021-22883 Référence CVE CVE-2021-22884 https://www.cve.org/CVERecord?id=CVE-2021-22884 Référence CVE CVE-2021-23358 https://www.cve.org/CVERecord?id=CVE-2021-23358 Référence CVE CVE-2021-27919 https://www.cve.org/CVERecord?id=CVE-2021-27919 Référence CVE CVE-2021-28363 https://www.cve.org/CVERecord?id=CVE-2021-28363 Référence CVE CVE-2021-29505 https://www.cve.org/CVERecord?id=CVE-2021-29505 Référence CVE CVE-2021-29921 https://www.cve.org/CVERecord?id=CVE-2021-29921 Référence CVE CVE-2021-31525 https://www.cve.org/CVERecord?id=CVE-2021-31525 Référence CVE CVE-2021-3177 https://www.cve.org/CVERecord?id=CVE-2021-3177 Référence CVE CVE-2021-33503 https://www.cve.org/CVERecord?id=CVE-2021-33503 Gestion détaillée du document le 29 juin 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

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-004626Python 用 urllib3 library における証明書検証に関する脆弱性

Python 用 urllib3 library には、証明書検証に関する脆弱性が存在します。

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.
Fix availability varies by product
Affected
Fixed
Update to V3.1.5 or later version
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
A mitigation or workaround reference is available from the source linked below; validate it against the affected product and version.
04

Evidence and provenance

Published 15 Mar 2021 · Last source change 3 Aug 2024, 21:40 UTC · CWE-295 · Improper Certificate Validation

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-2021-0457
Product sourceVendor CSAF · Siemens ProductCERT
Remediation sourceVendor CSAF · Siemens ProductCERT
CWE sourceNIST NVD
NVD statusNVD modified after enrichment

Missing structured fields: affected product. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    n/a · 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
    n/a · Fixed: Update to V3.1.5 or later version
    Siemens ProductCERT ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2021-0457↗Siemens ProductCERT security advisory · Siemens SSA-398330↗CVE authority or vendor reference↗Patch or update reference↗Patch or update reference↗Mitigation reference · GitHub GHSA-5PHF-PP7P-VC2R↗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-2021-28363 · cve.blacktree.nl