LiveActive security incident?Get immediate response
CVE Record

CVE-2021-28676: An issue was discovered in Pillow before 8.2.0.

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.

UnknownCVSS not scoredNot KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Pillow before 8.2.0 can get stuck while loading specially formed FLI image data. The business impact is availability: an image-processing service could consume worker time and stop responding if it accepts affected files. The provided sources do not show data theft, code execution, or active exploitation.

Executive priority

Treat this as a targeted availability risk, not a breach-class emergency based on the supplied evidence. Prioritize internet-facing or automated image-processing systems first, then clear remaining vulnerable Pillow versions through normal patch management.

Technical view

CVE-2021-28676 is a denial-of-service flaw in Pillow's FliDecode handling. For FLI data, the decoder did not ensure the block advance value was non-zero, which could cause an infinite loop during image load. Pillow 8.2.0 release notes and the upstream PR/commit document the fix.

Likely exposure

Exposure is most likely in applications using Pillow before 8.2.0 to process FLI images or untrusted image uploads. Internet-facing upload pipelines, background thumbnailers, and document conversion workers deserve priority review. Evidence in the bundle does not identify affected downstream products beyond Pillow packaging advisories.

Exploitation context

The bundle does not report active exploitation, and KEV is false. Exploitation would require getting vulnerable Pillow code to load malicious or malformed FLI data. The likely outcome described by sources is denial of service through an infinite loop, not compromise of confidentiality or integrity.

Researcher notes

The key condition is FLI decoding with a zero block advance leading to non-termination. Review upstream PR 5377 and commit bb6c11f for patch context and regression expectations. No CVSS, CWE, or exploit-in-the-wild evidence is included in the supplied bundle.

Mitigation direction

  • Upgrade Pillow to 8.2.0 or later where directly managed.
  • Apply distribution security updates for packaged Pillow deployments.
  • Restrict untrusted FLI image processing where immediate upgrade is delayed.
  • Check vendor guidance for backported fixes in supported operating systems.

Validation and detection

  • Inventory applications and images using Pillow before 8.2.0.
  • Identify services that accept or transform untrusted image files.
  • Confirm runtime package versions after dependency or OS updates.
  • Review deployment logs for stuck image-processing workers or timeouts.
Prepared
Confidence
high
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-28676 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
7Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.