CVE-2026-8946Network attack vector

Unspecified impact via Web Codecs boundary error

Published May 19, 2026 · Updated May 19, 2026

Incorrect boundary conditions in Mozilla Web Codecs in Firefox and Thunderbird allow attackers to cause unspecified impact via unspecified vectors. Mozilla has not disclosed the affected function, faulty boundary comparison, or operation performed on untrusted media input. Firefox before 151 and Firefox ESR before 115.36 or 140.11 on their respective branches are affected, as are Thunderbird before 151 and Thunderbird ESR before 140.11; Thunderbird disables scripting while reading mail.

CVSS severity7.5
High
EPSS probability0.56%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect boundary conditions in Mozilla Web Codecs in Firefox and Thunderbird allow attackers to cause unspecified impact via unspecified vectors. Mozilla has not disclosed the affected function, faulty boundary comparison, or operation performed on untrusted media input. Firefox before 151 and Firefox ESR before 115.36 or 140.11 on their respective branches are affected, as are Thunderbird before 151 and Thunderbird ESR before 140.11; Thunderbird disables scripting while reading mail.

The record

CVE
CVE-2026-8946
Published
May 19, 2026
Updated
May 19, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, CWE-119
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 19, 2026CVE publishedPublication date reported by the CVE source.
  2. May 19, 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

7.5redhat-SADPCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
8.8Amazon LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.5Oracle LinuxCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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-787Out-of-bounds Write
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer

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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