Firefox: Out-of-bounds Read
CVE-2026-2771 is a critical-severity out-of-bounds read vulnerability in Firefox from Mozilla, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. There is no confirmed exploitation so far. EPSS estimates a 0.76% chance of exploitation within 30 days, higher than 56% of scored CVEs.
Critical severity: a successful attack would have severe impact.
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.
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
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- 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:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | NVD |
| CVSS 3.1 | 9.8 | Critical | CISA (ADP) |
| CVSS 3.1 | 7.5 | High | CNA |
Official description
Undefined behavior in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer.
How developers prevent this class of flaw
- Use a language that provides appropriate memory abstractions.
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=2014593Issue Tracking, Permissions Required
- access.redhat.com/errata/RHSA-2026:3338
- access.redhat.com/errata/RHSA-2026:3339
- access.redhat.com/errata/RHSA-2026:3361
- access.redhat.com/errata/RHSA-2026:3491
- access.redhat.com/errata/RHSA-2026:3492
- access.redhat.com/errata/RHSA-2026:3493
- access.redhat.com/errata/RHSA-2026:3494
- access.redhat.com/errata/RHSA-2026:3495
- access.redhat.com/errata/RHSA-2026:3496
- access.redhat.com/errata/RHSA-2026:3497
- access.redhat.com/errata/RHSA-2026:3515
- access.redhat.com/errata/RHSA-2026:3516
- access.redhat.com/errata/RHSA-2026:3517
- access.redhat.com/errata/RHSA-2026:3976
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 Out-of-bounds Read vulnerabilities
- 7.8 High severity
- 9.1 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
- 7.5 High severity
- 9.8 Critical severity
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