CVE-2021-23437Network attack vector

Process denial of service via unbounded color regex

Published Sep 3, 2021 · Updated Sep 16, 2024

Regular expression denial of service in Pillow 5.2.0 through 8.3.1 allows attackers to hang a consuming process via a crafted color string. ImageColor.getrgb() applies color-format regular expressions to unbounded input without first limiting the color specifier's length. Exploitation requires an application to pass attacker-controlled color text to getrgb(), consuming CPU and delaying or hanging that process.

CVSS severity7.5
High
EPSS probability3.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in Pillow 5.2.0 through 8.3.1 allows attackers to hang a consuming process via a crafted color string. ImageColor.getrgb() applies color-format regular expressions to unbounded input without first limiting the color specifier's length. Exploitation requires an application to pass attacker-controlled color text to getrgb(), consuming CPU and delaying or hanging that process.

The record

CVE
CVE-2021-23437
Published
Sep 3, 2021
Updated
Sep 16, 2024
Vendor
Pillow
Product
Pillow
Classifications
CWE-400, CWE-125, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 3, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <unspecified
  2. Affected versionversion=unspecified <8.3.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Pillow · Pillowversion=0 <unspecified; version=unspecified <8.3.2

Published CVSS scores

7.5SnykCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
CWE-125Out-of-bounds Read
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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