CVE-2021-3902: Dompdf/dompdf Improper Restriction Of XML External Vulnerability

CRITICAL
Advisory Identifier: GHSA-3vjh-xrhf-v9xh
Share
CVSS 9.8
CWE-611
Published
Advisory Summary

CVE-2021-3902 is a CRITICAL (CVSS 9.8) improper restriction of xml external vulnerability (CWE-611: Improper Restriction of XML External Entity Reference) affecting Dompdf/dompdf libraries in the Packagist ecosystem. The issue involves improper restriction of xml external entity reference in dompdf/dompdf. Remediation is available by upgrading affected packages to version 2.0.0.

CVE-2021-3902 at a Glance

CVE Identifier CVE-2021-3902
GHSA Identifier GHSA-3vjh-xrhf-v9xh
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-611: Improper Restriction of XML External Entity Reference
Affected Product Dompdf/dompdf
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 9.8

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:H/A:H).

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 High (I:H)
Availability High (A:H)

How to Fix CVE-2021-3902

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

dompdf/dompdf fixed: 2.0.0 
Upgrade dompdf/dompdf to 2.0.0
Verify Direct and Transitive Dependencies

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

inspect dependencies for dompdf/dompdf

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-3902, inspect your project dependencies for Dompdf/dompdf:

inspect dependencies for dompdf/dompdf

Analyze the terminal output to locate any version of Dompdf/dompdf in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.0.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

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 Dompdf/dompdf, 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 improper restriction of external entities (XXE) vulnerability in dompdf/dompdf's SVG parser allows for Server-Side Request Forgery (SSRF) and deserialization attacks. This issue affects all versions prior to 2.0.0. The vulnerability can be exploited even if the isRemoteEnabled option is set to false. It allows attackers to perform SSRF, disclose internal image files, and cause PHAR deserialization attacks.

CVE-2021-3902 Affected Dompdf/dompdf Versions

1 component(s)
Fixed Versions:
2.0.0
Product / Package Ecosystem Affected Versions Fixed Version
dompdf/dompdf
 Packagist
< 2.0.0
2.0.0

References

NVD — CVE-2021-3902 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-3902
Security Fix Commit FIX COMMIT
https://github.com/dompdf/dompdf/commit/f56bc8e40be6c0ae0825e6c7396f4db80620b799
Dompdf/dompdf Source Repository REPOSITORY
https://github.com/dompdf/dompdf
huntr.com/bounties/a6071c07-8... WEB
https://huntr.com/bounties/a6071c07-806f-429a-8656-a4742e4191b1

Frequently Asked Questions

What is CVE-2021-3902?
CVE-2021-3902 is a security vulnerability in Dompdf/dompdf involving Improper Restriction of XML External Entity Reference in dompdf/dompdf under CWE-611: Improper Restriction of XML External Entity Reference.
Which Dompdf/dompdf versions are affected?
Affected versions include releases prior to 2.0.0 across affected packages: dompdf/dompdf.
What version fixes CVE-2021-3902?
Upgrading to 2.0.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is dompdf/dompdf affected?
Yes, dompdf/dompdf is affected in releases prior to 2.0.0. Upgrade your dependency to 2.0.0 or later.
What is the CVSS score of CVE-2021-3902?
CVE-2021-3902 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-3902?
CVE-2021-3902 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 Packagist dependencies for CVE-2021-3902?
Run the dependency tree command: 'inspect dependencies for dompdf/dompdf'. 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-3vjh-xrhf-v9xh",
  "modified" : "2024-11-18T21:23:28Z",
  "published" : "2024-11-15T12:31:44Z",
  "aliases" : [ "CVE-2021-3902" ],
  "summary" : "Improper Restriction of XML External Entity Reference in dompdf/dompdf",
  "details" : "An improper restriction of external entities (XXE) vulnerability in dompdf/dompdf's SVG parser allows for Server-Side Request Forgery (SSRF) and deserialization attacks. This issue affects all versions prior to 2.0.0. The vulnerability can be exploited even if the isRemoteEnabled option is set to false. It allows attackers to perform SSRF, disclose internal image files, and cause PHAR deserialization attacks.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "dompdf/dompdf"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.0.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-3902"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/dompdf/dompdf/commit/f56bc8e40be6c0ae0825e6c7396f4db80620b799"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/dompdf/dompdf"
  }, {
    "type" : "WEB",
    "url" : "https://huntr.com/bounties/a6071c07-806f-429a-8656-a4742e4191b1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-611" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2024-11-15T20:49:33Z",
    "nvd_published_at" : "2024-11-15T11:15:06Z"
  }
}