CVE-2021-43545Public exploitNetwork attack vector

Application denial of service via unthrottled reloads

Published Dec 8, 2021 · Updated Aug 4, 2024

Denial of service in Firefox before 95, Firefox ESR before 91.4.0, and Thunderbird before 91.4.0 allows remote attackers to hang or crash them. The DOM navigation code rate-limits ordinary Location API navigation but did not throttle location.reload(), so a tight script loop flooded the parent process and exhausted memory. Execution requires a user to load attacker-controlled active content; Thunderbird disables scripting while reading mail, limiting exposure through ordinary messages.

CVSS severity6.5
Medium
EPSS probability1.60%
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 Firefox before 95, Firefox ESR before 91.4.0, and Thunderbird before 91.4.0 allows remote attackers to hang or crash them. The DOM navigation code rate-limits ordinary Location API navigation but did not throttle location.reload(), so a tight script loop flooded the parent process and exhausted memory. Execution requires a user to load attacker-controlled active content; Thunderbird disables scripting while reading mail, limiting exposure through ordinary messages.

The record

CVE
CVE-2021-43545
Published
Dec 8, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-834, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 8, 2021CVE 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <95

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <95
Mozilla · Thunderbirdversion=unspecified <91.4.0
Mozilla · Firefox ESRversion=unspecified <91.4.0

Published CVSS scores

6.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
4.3NIST National Vulnerability DatabaseAV:N/AC:M/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-834Excessive Iteration
T1499Endpoint Denial of Service

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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