CVE-2023-4241Network attack vector

Application crash via stale end-tag parser state

Published Aug 16, 2023 · Updated Oct 2, 2024

Improper input validation in Cloudflare LOL HTML before 1.1.1 allows remote attackers to crash consuming applications via crafted HTML. TagScanner fails to reset is_in_end_tag when switching parsers, leaving stale state that triggers a panic on particular tag sequences. Exposure requires an application to process attacker-controlled HTML; the bounded consequence is interruption of that consuming process.

CVSS severity7.5
High
EPSS probability0.69%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Cloudflare LOL HTML before 1.1.1 allows remote attackers to crash consuming applications via crafted HTML. TagScanner fails to reset is_in_end_tag when switching parsers, leaving stale state that triggers a panic on particular tag sequences. Exposure requires an application to process attacker-controlled HTML; the bounded consequence is interruption of that consuming process.

The record

CVE
CVE-2023-4241
Published
Aug 16, 2023
Updated
Oct 2, 2024
Vendor
Cloudflare
Product
LOL HTML
Classifications
CWE-20, CAPEC-130, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 16, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 2, 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 <1.1.1
  2. Affected versionversion=0 <1.1.1 changes=[{"at":"1.1.1","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cloudflare · LOL HTMLversion=0 <1.1.1; version=0 <1.1.1 changes=[{"at":"1.1.1","status":"unaffected"}]

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5Cloudflare, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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-20Improper Input Validation
CAPEC-130Excessive Allocation
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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