CVE-2021-28363: Urllib3 Using Default SSLContext For HTTPS Vulnerability

Q: What is CVE-2021-28363?

CVE-2021-28363 is a security vulnerability in Urllib3 involving Using default SSLContext for HTTPS requests in an HTTPS proxy doesn't verify certificate hostname for proxy connection under CWE-295: Improper Certificate Validation.

Q: Which Urllib3 versions are affected?

Affected versions include releases prior to 1.26.4 across affected packages: urllib3.

Q: What version fixes CVE-2021-28363?

Upgrading to 1.26.4 (or the latest patched release for your respective branch) resolves the vulnerability.

Q: Is urllib3 affected?

Yes, urllib3 is affected in releases prior to 1.26.4. Upgrade your dependency to 1.26.4 or later.

Q: What is the CVSS score of CVE-2021-28363?

CVE-2021-28363 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

Q: What CWE is associated with CVE-2021-28363?

CVE-2021-28363 is classified under CWE-295: Improper Certificate Validation (The product does not validate, or incorrectly validates, a certificate.).

Q: How can I check PyPI dependencies for CVE-2021-28363?

Run the dependency tree command: 'pip show urllib3'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

MODERATE

Advisory Identifier: GHSA-5phf-pp7p-vc2r

CVSS 6.5

CWE-295

Published 2021-03-19

Advisory Summary

CVE-2021-28363 is a MODERATE (CVSS 6.5) using default sslcontext for https vulnerability (CWE-295: Improper Certificate Validation) affecting Urllib3 libraries in the PyPI ecosystem. The issue involves using default sslcontext for https requests in an https proxy doesn't verify certificate hostname for proxy connection. Remediation is available by upgrading affected packages to version 1.26.4.

CVE-2021-28363 at a Glance

CVE Identifier CVE-2021-28363

GHSA Identifier GHSA-5phf-pp7p-vc2r

Severity MODERATE

CVSS v3.1 Base Score 6.5

CWE Classification CWE-295: Improper Certificate Validation

Affected Product Urllib3

Package Ecosystem PyPI

Published Date 2021-03-19

Last Updated 2024-11-18

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N).

Attack Vector Network (AV:N)

Attack Complexity Low (AC:L)

Privileges Required None (PR:N)

User Interaction None (UI:N)

Scope Unchanged (S:U)

Confidentiality Low (C:L)

Integrity Low (I:L)

Availability None (A:N)

How to Fix CVE-2021-28363

To remediate this vulnerability, upgrade all affected Urllib3 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

urllib3 fixed: 1.26.4

pip install urllib3>=1.26.4

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release:

pip show urllib3

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-28363, inspect your installed packages using pip:

pip show urllib3

Analyze the terminal output to locate any version of Urllib3 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.26.4), your application is affected.

Note: The pip show urllib3 command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-295: Improper Certificate Validation, where the product does not validate, or incorrectly validates, a certificate. In Urllib3, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Users who are using an HTTPS proxy to issue HTTPS requests and haven't configured their own SSLContext via `proxy_config`. Only the default SSLContext is impacted. ### Patches [urllib3 >=1.26.4 has the issue resolved](https://github.com/urllib3/urllib3/releases/tag/1.26.4). urllib3<1.26 is not impacted due to not supporting HTTPS requests via HTTPS proxies. ### Workarounds Upgrading is recommended as this is a minor release and not likely to break current usage. Configuring an `SSLContext` with `check_hostname=True` and passing via `proxy_config` instead of relying on the default `SSLContext` ### For more information If you have any questions or comments about this advisory: * Email us at [sethmichaellarson@gmail.com](mailto:sethmichaellarson@gmail.com)

CVE-2021-28363 Affected Urllib3 Versions

1 component(s)

Fixed Versions:

1.26.4

Product / Package	Ecosystem	Affected Versions	Fixed Version
urllib3 pypi/urllib3	PyPI	≥ 1.26.0 < 1.26.4	1.26.4

References

GitHub Advisory / Wiki ADVISORY

https://github.com/urllib3/urllib3/security/advisories/GHSA-5phf-pp7p-vc2r

NVD — CVE-2021-28363 NVD

https://nvd.nist.gov/vuln/detail/CVE-2021-28363

Security Fix Commit FIX COMMIT

https://github.com/urllib3/urllib3/commit/8d65ea1ecf6e2cdc27d42124e587c1b83a3118b0

Urllib3 Source Repository REPOSITORY

https://github.com/pypa/advisory-database/tree/main/vulns/urllib3/PYSEC-2021-59.yaml

Urllib3 Source Repository REPOSITORY

https://github.com/pypa/advisory-db/tree/main/vulns/urllib3/PYSEC-2021-59.yaml

Urllib3 Source Repository REPOSITORY

https://github.com/urllib3/urllib3

Urllib3 Source Repository REPOSITORY

https://github.com/urllib3/urllib3/blob/main/CHANGES.rst#1264-2021-03-15

Urllib3 Source Repository REPOSITORY

https://github.com/urllib3/urllib3/commits/main

Urllib3 Release RELEASE

https://github.com/urllib3/urllib3/releases/tag/1.26.4

lists.fedoraproject.org/archives/list/packa... WEB

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4S65ZQVZ2ODGB52IC7VJDBUK4M5INCXL

lists.fedoraproject.org/archives/list/packa... WEB

https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4S65ZQVZ2ODGB52IC7VJDBUK4M5INCXL

pypi.org/project/urllib3/1.2... WEB

https://pypi.org/project/urllib3/1.26.4

Urllib3 Security Information SECURITY

https://security.gentoo.org/glsa/202107-36

Urllib3 Security Information SECURITY

https://security.gentoo.org/glsa/202305-02

Urllib3 Security Information SECURITY

https://security.netapp.com/advisory/ntap-20240621-0007

Urllib3 Security Information SECURITY

https://www.oracle.com/security-alerts/cpuoct2021.html

Frequently Asked Questions

What is CVE-2021-28363?

CVE-2021-28363 is a security vulnerability in Urllib3 involving Using default SSLContext for HTTPS requests in an HTTPS proxy doesn't verify certificate hostname for proxy connection under CWE-295: Improper Certificate Validation.

Which Urllib3 versions are affected?

Affected versions include releases prior to 1.26.4 across affected packages: urllib3.

What version fixes CVE-2021-28363?

Upgrading to 1.26.4 (or the latest patched release for your respective branch) resolves the vulnerability.

Is urllib3 affected?

Yes, urllib3 is affected in releases prior to 1.26.4. Upgrade your dependency to 1.26.4 or later.

What is the CVSS score of CVE-2021-28363?

CVE-2021-28363 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

What CWE is associated with CVE-2021-28363?

CVE-2021-28363 is classified under CWE-295: Improper Certificate Validation (The product does not validate, or incorrectly validates, a certificate.).

How can I check PyPI dependencies for CVE-2021-28363?

Run the dependency tree command: 'pip show urllib3'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

Machine-readable OSV JSON OSV v1.5 Schema

Normalized schema output

View Raw JSON

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5phf-pp7p-vc2r",
  "modified" : "2024-11-18T22:42:40Z",
  "published" : "2021-03-19T19:42:11Z",
  "aliases" : [ "CVE-2021-28363" ],
  "summary" : "Using default SSLContext for HTTPS requests in an HTTPS proxy doesn't verify certificate hostname for proxy connection",
  "details" : "### Impact\n\nUsers who are using an HTTPS proxy to issue HTTPS requests and haven't configured their own SSLContext via `proxy_config`.\nOnly the default SSLContext is impacted.\n\n### Patches\n\n[urllib3 >=1.26.4 has the issue resolved](https://github.com/urllib3/urllib3/releases/tag/1.26.4). urllib3<1.26 is not impacted due to not supporting HTTPS requests via HTTPS proxies.\n\n### Workarounds\n\nUpgrading is recommended as this is a minor release and not likely to break current usage.\n\nConfiguring an `SSLContext` with `check_hostname=True` and passing via `proxy_config` instead of relying on the default `SSLContext`\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Email us at [sethmichaellarson@gmail.com](mailto:sethmichaellarson@gmail.com)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "urllib3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.26.0"
      }, {
        "fixed" : "1.26.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/urllib3/urllib3/security/advisories/GHSA-5phf-pp7p-vc2r"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-28363"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/urllib3/urllib3/commit/8d65ea1ecf6e2cdc27d42124e587c1b83a3118b0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/urllib3/PYSEC-2021-59.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-db/tree/main/vulns/urllib3/PYSEC-2021-59.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/urllib3/urllib3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/urllib3/urllib3/blob/main/CHANGES.rst#1264-2021-03-15"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/urllib3/urllib3/commits/main"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/urllib3/urllib3/releases/tag/1.26.4"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4S65ZQVZ2ODGB52IC7VJDBUK4M5INCXL"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4S65ZQVZ2ODGB52IC7VJDBUK4M5INCXL"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/urllib3/1.26.4"
  }, {
    "type" : "WEB",
    "url" : "https://security.gentoo.org/glsa/202107-36"
  }, {
    "type" : "WEB",
    "url" : "https://security.gentoo.org/glsa/202305-02"
  }, {
    "type" : "WEB",
    "url" : "https://security.netapp.com/advisory/ntap-20240621-0007"
  }, {
    "type" : "WEB",
    "url" : "https://www.oracle.com/security-alerts/cpuoct2021.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-295" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-03-19T19:41:48Z",
    "nvd_published_at" : "2021-03-15T18:15:00Z"
  }
}

CVSS V3

6.5 MODERATE

Attack Vector Network (AV:N)

Attack Complexity Low (AC:L)

Privileges Required None (PR:N)

User Interaction None (UI:N)

Scope Unchanged (S:U)

Confidentiality Low (C:L)

Integrity Low (I:L)

Availability None (A:N)

Vector String

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Advisory Metadata

Source ID: GHSA-5phf-pp7p-vc2r
Schema Version: 1.4.0
Published: 2021-03-19 19:42
Last Modified: 2024-11-18 22:42
Database Record File: advisories/github-reviewed/2021/03/GHSA-5phf-pp7p-vc2r/GHSA-5phf-pp7p-vc2r.json