CVE-2021-29421: Pikepdf Improper Restriction Of XML External Vulnerability

HIGH
Advisory Identifier: GHSA-ccgm-3xw4-h5p8
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CVSS 7.5
CWE-611
Published
Advisory Summary

CVE-2021-29421 is a HIGH (CVSS 7.5) improper restriction of xml external vulnerability (CWE-611: Improper Restriction of XML External Entity Reference) affecting Pikepdf libraries in the PyPI ecosystem. The issue involves improper restriction of xml external entity reference in pikepdf. Remediation is available by upgrading affected packages to version 2.10.0.

CVE-2021-29421 at a Glance

CVE Identifier CVE-2021-29421
GHSA Identifier GHSA-ccgm-3xw4-h5p8
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-611: Improper Restriction of XML External Entity Reference
Affected Product Pikepdf
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-2021-29421

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

pikepdf fixed: 2.10.0 
pip install pikepdf>=2.10.0
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 pikepdf

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-29421, inspect your installed packages using pip:

pip show pikepdf

Analyze the terminal output to locate any version of Pikepdf in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.10.0), your application is affected.

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-611: Improper Restriction of XML External Entity Reference, where the product processes an xml document that can contain xml entities with uris that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. In Pikepdf, 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

models/metadata.py in the pikepdf package 1.3.0 through 2.9.2 for Python allows XXE when parsing XMP metadata entries.

CVE-2021-29421 Affected Pikepdf Versions

1 component(s)
Fixed Versions:
2.10.0
Product / Package Ecosystem Affected Versions Fixed Version
pikepdf
pypi/pikepdf
PyPI
≥ 1.3.0
< 2.10.0
2.10.0

References

NVD — CVE-2021-29421 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-29421
Security Fix Commit FIX COMMIT
https://github.com/pikepdf/pikepdf/commit/3f38f73218e5e782fe411ccbb3b44a793c0b343a
GitHub Advisory / Wiki ADVISORY
https://github.com/advisories/GHSA-ccgm-3xw4-h5p8
Pikepdf Source Repository REPOSITORY
https://github.com/pikepdf/pikepdf
Pikepdf Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/pikepdf/PYSEC-2021-34.yaml
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/36P4HTLBJPO524WMQWW57N3QRF4RFSJG
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/3QFLBBYGEDNXJ7FS6PIWTVI4T4BUPGEQ

Frequently Asked Questions

What is CVE-2021-29421?
CVE-2021-29421 is a security vulnerability in Pikepdf involving Improper Restriction of XML External Entity Reference in pikepdf under CWE-611: Improper Restriction of XML External Entity Reference.
Which Pikepdf versions are affected?
Affected versions include releases prior to 2.10.0 across affected packages: pikepdf.
What version fixes CVE-2021-29421?
Upgrading to 2.10.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pikepdf affected?
Yes, pikepdf is affected in releases prior to 2.10.0. Upgrade your dependency to 2.10.0 or later.
What is the CVSS score of CVE-2021-29421?
CVE-2021-29421 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-2021-29421?
CVE-2021-29421 is classified under CWE-611: Improper Restriction of XML External Entity Reference (The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.).
How can I check PyPI dependencies for CVE-2021-29421?
Run the dependency tree command: 'pip show pikepdf'. 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-ccgm-3xw4-h5p8",
  "modified" : "2024-10-09T19:51:42Z",
  "published" : "2021-04-20T16:30:03Z",
  "aliases" : [ "CVE-2021-29421" ],
  "summary" : "Improper Restriction of XML External Entity Reference in pikepdf",
  "details" : "models/metadata.py in the pikepdf package 1.3.0 through 2.9.2 for Python allows XXE when parsing XMP metadata entries.",
  "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" : "pikepdf"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.3.0"
      }, {
        "fixed" : "2.10.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-29421"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pikepdf/pikepdf/commit/3f38f73218e5e782fe411ccbb3b44a793c0b343a"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-ccgm-3xw4-h5p8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/pikepdf/pikepdf"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/pikepdf/PYSEC-2021-34.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/36P4HTLBJPO524WMQWW57N3QRF4RFSJG"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/3QFLBBYGEDNXJ7FS6PIWTVI4T4BUPGEQ"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-611" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-04-19T21:54:20Z",
    "nvd_published_at" : "2021-04-01T20:15:00Z"
  }
}