CVE-2021-39371: Pywps XML External Entity Injection Vulnerability

HIGH
Advisory Identifier: GHSA-p9wf-3xpg-c9g5
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CVSS 7.5
CWE-91 CWE-611
Published
Advisory Summary

CVE-2021-39371 is a HIGH (CVSS 7.5) xml external entity injection vulnerability (CWE-91: XML Injection (aka Blind XPath Injection)) affecting Pywps libraries in the PyPI ecosystem. The issue involves xml external entity injection in pywps. Remediation is available by upgrading affected packages to version 4.5.0.

CVE-2021-39371 at a Glance

CVE Identifier CVE-2021-39371
GHSA Identifier GHSA-p9wf-3xpg-c9g5
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-91: XML Injection (aka Blind XPath Injection)
Affected Product Pywps
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.5

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:H/I:N/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 High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2021-39371

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

pywps fixed: 4.5.0 
pip install pywps>=4.5.0
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 pywps

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-39371, inspect your installed packages using pip:

pip show pywps

Analyze the terminal output to locate any version of Pywps in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.5.0), your application is affected.

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-91: XML Injection (aka Blind XPath Injection), where the product does not properly neutralize special elements that are used in xml, allowing attackers to modify the syntax, content, or commands of the xml before it is processed by an end system. In Pywps, 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

An XML external entity (XXE) injection in PyWPS before 4.5.0 allows an attacker to view files on the application server filesystem by assigning a path to the entity. OWSLib 0.24.1 may also be affected.

CVE-2021-39371 Affected Pywps Versions

1 component(s)
Fixed Versions:
4.5.0
Product / Package Ecosystem Affected Versions Fixed Version
pywps
pypi/pywps
PyPI
< 4.5.0
4.5.0

References

NVD — CVE-2021-39371 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-39371
Pywps Source Repository REPOSITORY
https://github.com/geopython/OWSLib/issues/790
Pywps Source Repository REPOSITORY
https://github.com/geopython/pywps/pull/616
Security Fix Commit FIX COMMIT
https://github.com/geopython/pywps/commit/7d6b26a2e931df2feca0b7fb24f4d01610825aee
GitHub Advisory / Wiki ADVISORY
https://github.com/advisories/GHSA-p9wf-3xpg-c9g5
Pywps Source Repository REPOSITORY
https://github.com/geopython/pywps
Pywps Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/pywps/PYSEC-2021-121.yaml
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2021/09/msg00001.html

Frequently Asked Questions

What is CVE-2021-39371?
CVE-2021-39371 is a security vulnerability in Pywps involving XML External Entity Injection in PyWPS under CWE-91: XML Injection (aka Blind XPath Injection).
Which Pywps versions are affected?
Affected versions include releases prior to 4.5.0 across affected packages: pywps.
What version fixes CVE-2021-39371?
Upgrading to 4.5.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pywps affected?
Yes, pywps is affected in releases prior to 4.5.0. Upgrade your dependency to 4.5.0 or later.
What is the CVSS score of CVE-2021-39371?
CVE-2021-39371 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2021-39371?
CVE-2021-39371 is classified under CWE-91: XML Injection (aka Blind XPath Injection) (The product does not properly neutralize special elements that are used in XML, allowing attackers to modify the syntax, content, or commands of the XML before it is processed by an end system.).
How can I check PyPI dependencies for CVE-2021-39371?
Run the dependency tree command: 'pip show pywps'. 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-p9wf-3xpg-c9g5",
  "modified" : "2024-10-24T21:53:22Z",
  "published" : "2021-09-02T17:11:13Z",
  "aliases" : [ "CVE-2021-39371" ],
  "summary" : "XML External Entity Injection in PyWPS",
  "details" : "An XML external entity (XXE) injection in PyWPS before 4.5.0 allows an attacker to view files on the application server filesystem by assigning a path to the entity. OWSLib 0.24.1 may also be affected.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pywps"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.5.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-39371"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/geopython/OWSLib/issues/790"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/geopython/pywps/pull/616"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/geopython/pywps/commit/7d6b26a2e931df2feca0b7fb24f4d01610825aee"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-p9wf-3xpg-c9g5"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/geopython/pywps"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/pywps/PYSEC-2021-121.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2021/09/msg00001.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-611", "CWE-91" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-08-25T19:48:42Z",
    "nvd_published_at" : "2021-08-23T01:15:00Z"
  }
}