CVE-2022-31103Public exploitNetwork attack vector

Browser hang via recursive keyframe rule processing

Published Jun 27, 2022 · Updated Apr 23, 2025

Denial of service in Mat Sz lettersanitizer before 1.0.2 allows remote attackers to hang a browser through HTML containing @keyframes CSS. The sanitize function recursively processes any CSS rule exposing cssRules as though it were a media rule, so a keyframes rule traps processing until the browser consumes a full CPU core. Any application that passes attacker-controlled email HTML to sanitize() is exposed; the demonstrated consequence is 100 percent CPU use and an unresponsive browser page.

CVSS severity7.5
High
EPSS probability1.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Mat Sz lettersanitizer before 1.0.2 allows remote attackers to hang a browser through HTML containing @keyframes CSS. The sanitize function recursively processes any CSS rule exposing cssRules as though it were a media rule, so a keyframes rule traps processing until the browser consumes a full CPU core. Any application that passes attacker-controlled email HTML to sanitize() is exposed; the demonstrated consequence is 100 percent CPU use and an unresponsive browser page.

The record

CVE
CVE-2022-31103
Published
Jun 27, 2022
Updated
Apr 23, 2025
Vendor
Mat Sz
Product
lettersanitizer
Classifications
CWE-754, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 27, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 23, 2025Record 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=< 1.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mat Sz · lettersanitizerversion=< 1.0.2

Published CVSS scores

7.5GitHub, Inc.CVSS: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 exploitPublished

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

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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