CVE-2026-84124Network attack vector

Memory corruption via freed DOM object reuse

Published Sep 1, 2026 · Updated Sep 1, 2026

Use-after-free in Firefox before 155 and Thunderbird before 155 allows remote attackers to corrupt memory via crafted web content. Mozilla has not published the object lifetime error or code path that leaves a freed DOM Core & HTML object accessible to attacker-controlled content. Firefox ESR 140 before 140.15, Firefox ESR 153 before 153.2, and equivalent Thunderbird ESR branches are also affected; exploitation requires user interaction in a browser-like context, with low confidentiality and integrity impact and no availability impact.

CVSS severity5.4
Medium
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Use-after-free in Firefox before 155 and Thunderbird before 155 allows remote attackers to corrupt memory via crafted web content. Mozilla has not published the object lifetime error or code path that leaves a freed DOM Core & HTML object accessible to attacker-controlled content. Firefox ESR 140 before 140.15, Firefox ESR 153 before 153.2, and equivalent Thunderbird ESR branches are also affected; exploitation requires user interaction in a browser-like context, with low confidentiality and integrity impact and no availability impact.

The record

CVE
CVE-2026-84124
Published
Sep 1, 2026
Updated
Sep 1, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-416, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 1, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 1, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

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

5.4CISA ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/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.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1203Exploitation for Client Execution

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo