CVE-2021-3649Network attack vector

Browser hang via catastrophic email HTML regex

Published Jul 16, 2021 · Updated Aug 3, 2024

Inefficient regex processing in Chatwoot 1.11.1 and earlier allows remote attackers to hang an agent's browser via crafted email HTML. The stripStyleCharacters function applies globally repeated, ambiguous style-tag expressions to untrusted incoming email content, enabling catastrophic backtracking. A sender needs only a route into a configured email inbox; processing the conversation can monopolize browser execution and interrupt the agent interface.

CVSS severity7.5
High
EPSS probability1.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Inefficient regex processing in Chatwoot 1.11.1 and earlier allows remote attackers to hang an agent's browser via crafted email HTML. The stripStyleCharacters function applies globally repeated, ambiguous style-tag expressions to untrusted incoming email content, enabling catastrophic backtracking. A sender needs only a route into a configured email inbox; processing the conversation can monopolize browser execution and interrupt the agent interface.

The record

CVE
CVE-2021-3649
Published
Jul 16, 2021
Updated
Aug 3, 2024
Vendor
Chatwoot
Product
Chatwoot
Classifications
CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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 <=1.11.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Chatwoot · Chatwootversion=unspecified <=1.11.1

Published CVSS scores

5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NVDCVSS: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-1333Inefficient Regular Expression Complexity
T1499.004Application or System Exploitation

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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