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Not in CISA KEV
HIGH severity

CVE-2021-27921 — pillow

HIGHFix: python-pillow/Pillow@756fff3

CVE-2021-27921 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in pillow. A fix is available for pillow — see the affected versions and patch details below.

Pillow Denial of Service by Uncontrolled Resource Consumption

Also known asBIT-pillow-2021-27921GHSA-f4w8-cv6p-x6r5PYSEC-2021-40
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
3.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs88th percentile — riskier than 88% of all scored CVEsHighest risk
0.00%1.33%2.66%4.00%0.4%3.2%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-27921 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🐍pillow

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Pillow before 8.1.2 allows attackers to cause a denial of service (memory consumption) because the reported size of a contained image is not properly checked for a BLP container, and thus an attempted memory allocation can be very large.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIpillowall versions8.1.2pip install --upgrade 'pillow==8.1.2'

Affected Products

2 products · 4 configurations
OS
fedorafedoraproject
3 versions
323334
Application
pillowpython
< 8.1.1
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pillow, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update pillow to 8.1.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27921 is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate
Workaround published by Red Hat
Disable the invoice generation feature to mitigate this vulnerability in Red Hat Quay.
Source: Red Hat security advisory for CVE-2021-27921 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat Enterprise Linux 8python-pillow-0:5.1.1-16.el8RHSA-2021:4149
Red Hat Quay 3quay/quay-rhel8:v3.6.0-62RHSA-2021:3917
UbuntuHIGH
USN-4763-1Ubuntu

Frequently Asked Questions

Pillow before 8.1.2 allows attackers to cause a denial of service (memory consumption) because the reported size of a contained image is not properly checked for a BLP container, and thus an attempted memory allocation can be very large.
O3 Security · Impact-Aware SCA

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CVE-2021-27921: pillow DoS — Fixed in 8.1.2