CVE-2026-6766Network attack vector

Sensitive-data disclosure via undisclosed NSS boundary error

Published Apr 21, 2026 · Updated Apr 21, 2026

NSS boundary error in Mozilla Firefox and Thunderbird before 150, or before 140.10 for ESR, allows remote attackers to read sensitive data. Mozilla has not disclosed the affected NSS function, malformed input, or incorrect boundary operation; the linked bug is access-restricted. Network access without authentication or user interaction is sufficient, and the published assessment limits impact to confidentiality with no integrity or availability loss.

CVSS severity7.5
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NSS boundary error in Mozilla Firefox and Thunderbird before 150, or before 140.10 for ESR, allows remote attackers to read sensitive data. Mozilla has not disclosed the affected NSS function, malformed input, or incorrect boundary operation; the linked bug is access-restricted. Network access without authentication or user interaction is sufficient, and the published assessment limits impact to confidentiality with no integrity or availability loss.

The record

CVE
CVE-2026-6766
Published
Apr 21, 2026
Updated
Apr 21, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-754
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 21, 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

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
6.5Amazon LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
6.1Oracle LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/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-754Improper Check for Unusual or Exceptional Conditions

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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