CVE-2026-8391Network attack vector

Unspecified impact in JavaScript Engine

Published May 12, 2026 · Updated May 12, 2026

An unspecified JavaScript Engine issue in Mozilla Firefox and Thunderbird allows attackers to achieve an unspecified impact. Mozilla has not published the flawed operation, triggering input, or concrete security consequence, and the only technical Bugzilla report requires permission. Published assessments disagree on whether user interaction is required; Thunderbird disables scripting when reading mail, limiting email-based reachability.

CVSS severity5.3
Medium
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

An unspecified JavaScript Engine issue in Mozilla Firefox and Thunderbird allows attackers to achieve an unspecified impact. Mozilla has not published the flawed operation, triggering input, or concrete security consequence, and the only technical Bugzilla report requires permission. Published assessments disagree on whether user interaction is required; Thunderbird disables scripting when reading mail, limiting email-based reachability.

The record

CVE
CVE-2026-8391
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-20, CWE-475, CWE-79, CWE-119
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 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
5.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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-20Improper Input Validation
CWE-475Undefined Behavior for Input to API
CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
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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