CVE-2021-40897Public exploitNetwork attack vector

Service hang via HTML regex backtracking

Published Jun 27, 2022 · Updated Aug 4, 2024

Regular expression denial of service in split-html-to-chars 1.0.5 allows remote attackers to hang a consuming process via invalid HTML. During HTML splitting, an inefficient regular expression backtracks excessively over a long invalid declaration containing repeated quote characters. Exploitation requires an application to pass attacker-controlled HTML to the library; successful input consumes CPU and stalls processing.

CVSS severity7.5
High
EPSS probability1.05%
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 split-html-to-chars 1.0.5 allows remote attackers to hang a consuming process via invalid HTML. During HTML splitting, an inefficient regular expression backtracks excessively over a long invalid declaration containing repeated quote characters. Exploitation requires an application to pass attacker-controlled HTML to the library; successful input consumes CPU and stalls processing.

The record

CVE
CVE-2021-40897
Published
Jun 27, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 27, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST NVDCVSS: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.

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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-1333Inefficient Regular Expression Complexity
T1499.004Application 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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