CVE-2021-23346Public exploitNetwork attack vector

Process hang via backtracking tag parser regex

Published Mar 4, 2021 · Updated Sep 16, 2024

ReDoS in html-parse-stringify before 2.0.1 and all html-parse-stringify2 versions allows attackers to hang a process with crafted HTML. The parse.js tagRE pattern repeats quote-matching branches in a way that triggers excessive backtracking on long malformed tags containing repeated quotes. Any application that passes attacker-controlled HTML to the parse function can have its event-loop process frozen, while applications that never parse such input are not exposed.

CVSS severity4.8
Medium
EPSS probability2.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ReDoS in html-parse-stringify before 2.0.1 and all html-parse-stringify2 versions allows attackers to hang a process with crafted HTML. The parse.js tagRE pattern repeats quote-matching branches in a way that triggers excessive backtracking on long malformed tags containing repeated quotes. Any application that passes attacker-controlled HTML to the parse function can have its event-loop process frozen, while applications that never parse such input are not exposed.

The record

CVE
CVE-2021-23346
Published
Mar 4, 2021
Updated
Sep 16, 2024
Vendor
Henrik Joreteg
Product
html-parse-stringify
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 4, 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=unspecified <2.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Henrik Joreteg · html-parse-stringifyversion=unspecified <2.0.1
Ray Di Ciaccio · html-parse-stringify2version=0 <unspecified

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
4.8SnykCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

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-400Uncontrolled Resource Consumption
T1499.004Application or System Exploitation Flood

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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