CVE-2021-23437: Pillow Remote Code Execution Vulnerability

HIGH
Advisory Identifier: GHSA-98vv-pw6r-q6q4
Share
CVSS 7.5
CWE-125 CWE-400
Published
Advisory Summary

CVE-2021-23437 is a HIGH (CVSS 7.5) remote code execution vulnerability (CWE-125: Out-of-bounds Read) affecting Pillow libraries in the PyPI ecosystem. The issue involves uncontrolled resource consumption in pillow. Remediation is available by upgrading affected packages to version 8.3.2.

CVE-2021-23437 at a Glance

CVE Identifier CVE-2021-23437
GHSA Identifier GHSA-98vv-pw6r-q6q4
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-125: Out-of-bounds Read
Affected Product Pillow
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:N/I:N/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 None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2021-23437

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

pillow fixed: 8.3.2 
pip install pillow>=8.3.2
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 pillow

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-23437, inspect your installed packages using pip:

pip show pillow

Analyze the terminal output to locate any version of Pillow in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 8.3.2), your application is affected.

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-125: Out-of-bounds Read, where the product reads data past the end, or before the beginning, of the intended buffer. In Pillow, 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

The package pillow 5.2.0 and before 8.3.2 are vulnerable to Regular Expression Denial of Service (ReDoS) via the getrgb function.

CVE-2021-23437 Affected Pillow Versions

1 component(s)
Fixed Versions:
8.3.2
Product / Package Ecosystem Affected Versions Fixed Version
pillow
pypi/pillow
PyPI
≥ 5.2.0
< 8.3.2
8.3.2

References

NVD — CVE-2021-23437 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-23437
Security Fix Commit FIX COMMIT
https://github.com/python-pillow/Pillow/commit/9e08eb8f78fdfd2f476e1b20b7cf38683754866b
GitHub Advisory / Wiki ADVISORY
https://github.com/advisories/GHSA-98vv-pw6r-q6q4
Pillow Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/pillow/PYSEC-2021-317.yaml
Pillow Source Repository REPOSITORY
https://github.com/python-pillow/Pillow
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2024/03/msg00021.html
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RNSG6VFXTAROGF7ACYLMAZNQV4EJ6I2C
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VKRCL7KKAKOXCVD7M6WC5OKFGL4L3SJT
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/RNSG6VFXTAROGF7ACYLMAZNQV4EJ6I2C
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/VKRCL7KKAKOXCVD7M6WC5OKFGL4L3SJT
Pillow Release RELEASE
https://pillow.readthedocs.io/en/stable/releasenotes/8.3.2.html
Pillow Security Information SECURITY
https://security.gentoo.org/glsa/202211-10
snyk.io/vuln/snyk-python-pi... WEB
https://snyk.io/vuln/SNYK-PYTHON-PILLOW-1319443

Frequently Asked Questions

What is CVE-2021-23437?
CVE-2021-23437 is a security vulnerability in Pillow involving Uncontrolled Resource Consumption in pillow under CWE-125: Out-of-bounds Read.
Which Pillow versions are affected?
Affected versions include releases prior to 8.3.2 across affected packages: pillow.
What version fixes CVE-2021-23437?
Upgrading to 8.3.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pillow affected?
Yes, pillow is affected in releases prior to 8.3.2. Upgrade your dependency to 8.3.2 or later.
What is the CVSS score of CVE-2021-23437?
CVE-2021-23437 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:N/I:N/A:H.
What CWE is associated with CVE-2021-23437?
CVE-2021-23437 is classified under CWE-125: Out-of-bounds Read (The product reads data past the end, or before the beginning, of the intended buffer.).
How can I check PyPI dependencies for CVE-2021-23437?
Run the dependency tree command: 'pip show pillow'. 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-98vv-pw6r-q6q4",
  "modified" : "2024-10-09T21:02:05Z",
  "published" : "2021-09-07T23:08:10Z",
  "aliases" : [ "CVE-2021-23437" ],
  "summary" : "Uncontrolled Resource Consumption in pillow",
  "details" : "The package pillow 5.2.0 and before 8.3.2 are vulnerable to Regular Expression Denial of Service (ReDoS) via the getrgb function.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pillow"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.2.0"
      }, {
        "fixed" : "8.3.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-23437"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/python-pillow/Pillow/commit/9e08eb8f78fdfd2f476e1b20b7cf38683754866b"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-98vv-pw6r-q6q4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/pillow/PYSEC-2021-317.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/python-pillow/Pillow"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2024/03/msg00021.html"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RNSG6VFXTAROGF7ACYLMAZNQV4EJ6I2C"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VKRCL7KKAKOXCVD7M6WC5OKFGL4L3SJT"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/RNSG6VFXTAROGF7ACYLMAZNQV4EJ6I2C"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/VKRCL7KKAKOXCVD7M6WC5OKFGL4L3SJT"
  }, {
    "type" : "WEB",
    "url" : "https://pillow.readthedocs.io/en/stable/releasenotes/8.3.2.html"
  }, {
    "type" : "WEB",
    "url" : "https://security.gentoo.org/glsa/202211-10"
  }, {
    "type" : "WEB",
    "url" : "https://snyk.io/vuln/SNYK-PYTHON-PILLOW-1319443"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-125", "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-09-07T15:15:55Z",
    "nvd_published_at" : "2021-09-03T16:15:00Z"
  }
}