CVE-2020-11888: Markdown2 Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-fv3h-8x5j-pvgq
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CVSS 6.1
CWE-79
Published
Advisory Summary

CVE-2020-11888 is a MODERATE (CVSS 6.1) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Markdown2 libraries in the PyPI ecosystem. The issue involves xss in python-markdown2. Remediation is available by upgrading affected packages to version 2.3.9.

CVE-2020-11888 at a Glance

CVE Identifier CVE-2020-11888
GHSA Identifier GHSA-fv3h-8x5j-pvgq
Severity MODERATE
CVSS v3.1 Base Score 6.1
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Markdown2
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 6.1

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:R/S:C/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2020-11888

To remediate this vulnerability, upgrade all affected Markdown2 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

markdown2 fixed: 2.3.9 
pip install markdown2>=2.3.9
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 markdown2

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2020-11888, inspect your installed packages using pip:

pip show markdown2

Analyze the terminal output to locate any version of Markdown2 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.3.9), your application is affected.

Note: The pip show markdown2 command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Markdown2, 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

python-markdown2 through 2.3.8 allows XSS because element names are mishandled unless a \w+ match succeeds. For example, an attack might use elementname@ or elementname- with an onclick attribute.

CVE-2020-11888 Affected Markdown2 Versions

1 component(s)
Fixed Versions:
2.3.9
Product / Package Ecosystem Affected Versions Fixed Version
markdown2
pypi/markdown2
PyPI
< 2.3.9
2.3.9

References

NVD — CVE-2020-11888 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-11888
Markdown2 Source Repository REPOSITORY
https://github.com/trentm/python-markdown2/issues/348
Markdown2 Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/markdown2/PYSEC-2020-65.yaml
Markdown2 Source Repository REPOSITORY
https://github.com/trentm/python-markdown2
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/6XOAIRJJCZNJUALXDHSIGH5PS2H63A3J
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/AQLRBGRVRRZK7P5SFL2MNGXFX37YHJAV
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PN6QSHRFZXRQAYZJQ4MOW5MKIXBYOMED
Markdown2 Security Information SECURITY
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00031.html
Markdown2 Security Information SECURITY
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00035.html

Frequently Asked Questions

What is CVE-2020-11888?
CVE-2020-11888 is a security vulnerability in Markdown2 involving XSS in python-markdown2 under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Markdown2 versions are affected?
Affected versions include releases prior to 2.3.9 across affected packages: markdown2.
What version fixes CVE-2020-11888?
Upgrading to 2.3.9 (or the latest patched release for your respective branch) resolves the vulnerability.
Is markdown2 affected?
Yes, markdown2 is affected in releases prior to 2.3.9. Upgrade your dependency to 2.3.9 or later.
What is the CVSS score of CVE-2020-11888?
CVE-2020-11888 has a CVSS v3.1 base score of 6.1 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2020-11888?
CVE-2020-11888 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check PyPI dependencies for CVE-2020-11888?
Run the dependency tree command: 'pip show markdown2'. 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-fv3h-8x5j-pvgq",
  "modified" : "2024-09-24T20:27:32Z",
  "published" : "2020-04-22T20:59:50Z",
  "aliases" : [ "CVE-2020-11888" ],
  "summary" : "XSS in python-markdown2",
  "details" : "python-markdown2 through 2.3.8 allows XSS because element names are mishandled unless a \\w+ match succeeds. For example, an attack might use elementname@ or elementname- with an onclick attribute.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "markdown2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.3.9"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.3.8"
    }
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-11888"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/trentm/python-markdown2/issues/348"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/markdown2/PYSEC-2020-65.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/trentm/python-markdown2"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/6XOAIRJJCZNJUALXDHSIGH5PS2H63A3J"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/AQLRBGRVRRZK7P5SFL2MNGXFX37YHJAV"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PN6QSHRFZXRQAYZJQ4MOW5MKIXBYOMED"
  }, {
    "type" : "WEB",
    "url" : "http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00031.html"
  }, {
    "type" : "WEB",
    "url" : "http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00035.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-04-22T19:19:38Z",
    "nvd_published_at" : null
  }
}