CVE-2021-28676: Pillow Potential Infinite Loop Vulnerability

HIGH
Advisory Identifier: GHSA-7r7m-5h27-29hp
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CVSS 7.5
CWE-835
Published
Advisory Summary

CVE-2021-28676 is a HIGH (CVSS 7.5) potential infinite loop vulnerability (CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')) affecting Pillow libraries in the PyPI ecosystem. The issue involves potential infinite loop in pillow. Remediation is available by upgrading affected packages to version 8.2.0.

CVE-2021-28676 at a Glance

CVE Identifier CVE-2021-28676
GHSA Identifier GHSA-7r7m-5h27-29hp
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')
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-2021-28676

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: 8.2.0 
pip install pillow>=8.2.0
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 pillow

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-28676, 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 8.2.0), 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-835: Loop with Unreachable Exit Condition ('Infinite Loop'), where the product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. 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

An issue was discovered in Pillow before 8.2.0. For FLI data, FliDecode did not properly check that the block advance was non-zero, potentially leading to an infinite loop on load.

CVE-2021-28676 Affected Pillow Versions

1 component(s)
Fixed Versions:
8.2.0
Product / Package Ecosystem Affected Versions Fixed Version
pillow
pypi/pillow
PyPI
< 8.2.0
8.2.0

References

NVD — CVE-2021-28676 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-28676
Pillow Source Repository REPOSITORY
https://github.com/python-pillow/Pillow/pull/5377
Security Fix Commit FIX COMMIT
https://github.com/python-pillow/Pillow/commit/bb6c11fb889e6c11b0ee122b828132ee763b5856
GitHub Advisory / Wiki ADVISORY
https://github.com/advisories/GHSA-7r7m-5h27-29hp
Pillow Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/pillow/PYSEC-2021-92.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/2021/07/msg00018.html
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MQHA5HAIBOYI3R6HDWCLAGFTIQP767FL
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/MQHA5HAIBOYI3R6HDWCLAGFTIQP767FL
Pillow Release RELEASE
https://pillow.readthedocs.io/en/stable/releasenotes/8.2.0.html#cve-2021-28676-fix-fli-dos
Pillow Security Information SECURITY
https://security.gentoo.org/glsa/202107-33

Frequently Asked Questions

What is CVE-2021-28676?
CVE-2021-28676 is a security vulnerability in Pillow involving Potential infinite loop in Pillow under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop').
Which Pillow versions are affected?
Affected versions include releases prior to 8.2.0 across affected packages: pillow.
What version fixes CVE-2021-28676?
Upgrading to 8.2.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pillow affected?
Yes, pillow is affected in releases prior to 8.2.0. Upgrade your dependency to 8.2.0 or later.
What is the CVSS score of CVE-2021-28676?
CVE-2021-28676 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-2021-28676?
CVE-2021-28676 is classified under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop') (The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.).
How can I check PyPI dependencies for CVE-2021-28676?
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-7r7m-5h27-29hp",
  "modified" : "2024-10-11T20:41:37Z",
  "published" : "2021-06-08T18:48:53Z",
  "aliases" : [ "CVE-2021-28676" ],
  "summary" : "Potential infinite loop in Pillow",
  "details" : "An issue was discovered in Pillow before 8.2.0. For FLI data, FliDecode did not properly check that the block advance was non-zero, potentially leading to an infinite loop on load.",
  "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",
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  } ],
  "affected" : [ {
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    },
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    } ]
  } ],
  "references" : [ {
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  }, {
    "type" : "WEB",
    "url" : "https://github.com/python-pillow/Pillow/pull/5377"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/python-pillow/Pillow/commit/bb6c11fb889e6c11b0ee122b828132ee763b5856"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-7r7m-5h27-29hp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/pillow/PYSEC-2021-92.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/python-pillow/Pillow"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2021/07/msg00018.html"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MQHA5HAIBOYI3R6HDWCLAGFTIQP767FL"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/MQHA5HAIBOYI3R6HDWCLAGFTIQP767FL"
  }, {
    "type" : "WEB",
    "url" : "https://pillow.readthedocs.io/en/stable/releasenotes/8.2.0.html#cve-2021-28676-fix-fli-dos"
  }, {
    "type" : "WEB",
    "url" : "https://security.gentoo.org/glsa/202107-33"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-835" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-06-03T21:46:13Z",
    "nvd_published_at" : "2021-06-02T16:15:00Z"
  }
}