CVE-2021-23368Network attack vector

Processing hang via greedy source-map regex

Published Apr 12, 2021 · Updated Sep 16, 2024

Regular expression denial of service in PostCSS 7.0.0 through 7.0.35 and 8.0.0 through 8.2.9 allows remote attackers to hang CSS processing. PreviousMap.loadAnnotation and getAnnotationURL apply greedy sourceMappingURL comment patterns whose trailing whitespace repetition causes excessive backtracking on crafted CSS. The vulnerable path is reached only when a consuming application passes attacker-controlled CSS with source-map annotations; the resulting CPU exhaustion interrupts that application's processing.

CVSS severity5.3
Medium
EPSS probability3.54%
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 PostCSS 7.0.0 through 7.0.35 and 8.0.0 through 8.2.9 allows remote attackers to hang CSS processing. PreviousMap.loadAnnotation and getAnnotationURL apply greedy sourceMappingURL comment patterns whose trailing whitespace repetition causes excessive backtracking on crafted CSS. The vulnerable path is reached only when a consuming application passes attacker-controlled CSS with source-map annotations; the resulting CPU exhaustion interrupts that application's processing.

The record

CVE
CVE-2021-23368
Published
Apr 12, 2021
Updated
Sep 16, 2024
Vendor
PostCSS
Product
PostCSS
Classifications
CWE-400, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 12, 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=7.0.0 <unspecified
  2. Affected versionversion=unspecified <8.2.10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

PostCSS · PostCSSversion=7.0.0 <unspecified; version=unspecified <8.2.10

Published CVSS scores

5.3SnykCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV: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
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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