CVE-2026-74938Network attack vector

Confidentiality and integrity compromise via mitigation bypass

Published Aug 18, 2026 · Updated Aug 18, 2026

Mitigation bypass in Mozilla Firefox and Thunderbird before 154 and their ESR editions before 153.1 allows remote attackers to read or alter data. The flaw is in the JavaScript garbage collector, but Mozilla has not published which mitigation is bypassed or the incorrect operation that permits the bypass. No privileges or user interaction are required in browser contexts; Thunderbird generally disables scripting while reading email, limiting ordinary mail-based reachability.

CVSS severity9.1
Critical
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Mitigation bypass in Mozilla Firefox and Thunderbird before 154 and their ESR editions before 153.1 allows remote attackers to read or alter data. The flaw is in the JavaScript garbage collector, but Mozilla has not published which mitigation is bypassed or the incorrect operation that permits the bypass. No privileges or user interaction are required in browser contexts; Thunderbird generally disables scripting while reading email, limiting ordinary mail-based reachability.

The record

CVE
CVE-2026-74938
Published
Aug 18, 2026
Updated
Aug 18, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-693
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 18, 2026Record 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

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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.

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-693Protection Mechanism Failure

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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