Answer in brief
CVE-2026-2771 records a Critical severity (CVSS 9.8) vulnerability in Undefined behavior in the DOM: Core & HTML component. The current sources do not mark it as known exploited. The current feed maps Red Hat/rhel10/firefox-flatpak (generic), Red Hat/rhel10/thunderbird-flatpak (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 9.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Red Hat/rhel10/firefox-flatpak (generic), Red Hat/rhel10/thunderbird-flatpak (generic). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:* | Not reported | Not reported |
| cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:* | Not reported | Not reported |
| cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:* | Not reported | Not reported |
| cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| Red Hat/rhel10/firefox-flatpakgeneric | * | Not reported |
| Red Hat/rhel10/thunderbird-flatpakgeneric | * | Not reported |
Published upstream
Feb 24, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 21, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 15, 2026
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.
Quoted source text, attributed separately from HOL analysis.