Review reviewHigh

CVE-2026-16405

Mozilla Firefox, Thunderbird, firefox

Information disclosure in the Networking: WebSockets component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

CVSS
7.5
EPSS
0.26%
17.2% percentile
CISA KEV
Not listed
Published
2026.07.21
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.26%
Technical severityCVSS 7.5

Vulnerability overview

Information disclosure in the Networking: WebSockets component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

Affected product and versions

Product
Mozilla Firefox, Thunderbird, firefox
Affected versions
< 153.0.0, >= 140.1.0 < 140.13.0
Fixed versions
153.0.0, 140.13.0

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Mozilla Firefox, Thunderbird, firefox and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CWE
CWE-200
CVE-2026-16405 — Mozilla Firefox, Thunderbird, firefox | SECUFOCUS NOW