Firefox: Protection Mechanism Failure
CVE-2026-8401 is a high-severity protection mechanism failure vulnerability in Firefox from Mozilla, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. There is no confirmed exploitation so far. EPSS estimates a 0.31% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of Firefox you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on mozilla.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by CNA.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | CISA (ADP) |
| CVSS 3.1 | 7.5 | High | CNA |
Official description
Sandbox escape in the Profile Backup component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Protection Mechanism Failure
The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other references
- bugzilla.mozilla.org/show_bug.cgi?id=2038679Permissions Required
- access.redhat.com/errata/RHSA-2026:21378
- access.redhat.com/errata/RHSA-2026:21380
- access.redhat.com/errata/RHSA-2026:21381
- access.redhat.com/errata/RHSA-2026:21382
- access.redhat.com/errata/RHSA-2026:22325
- access.redhat.com/errata/RHSA-2026:22643
- access.redhat.com/errata/RHSA-2026:26174
- access.redhat.com/errata/RHSA-2026:26268
- access.redhat.com/errata/RHSA-2026:26269
- access.redhat.com/errata/RHSA-2026:26270
- access.redhat.com/errata/RHSA-2026:26491
- access.redhat.com/errata/RHSA-2026:26492
- access.redhat.com/errata/RHSA-2026:26493
- access.redhat.com/errata/RHSA-2026:26521
Other vulnerabilities in Firefox
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
Recent Protection Mechanism Failure vulnerabilities
- 8.8 High severity
- 7.5 High severity
- 8.1 High severity
- 8.1 High severity
- 8.3 High severity
- 7.8 High severity
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