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No exploitation reported

CVE-2026-109740

Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component

No exploitation reported by the sources we read.

  • Published2026-10-13
  • WeaknessCWE-119

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.

Timeline

dates in UTC
  1. 2026-10-1313:17CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-109740?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-109740?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • CVE-2026-109740 Red Hat Product Security23 known affected

    firefox: firefox: Sandbox escape via incorrect boundary conditions in Win32 widget

    firefox as a component of Red Hat Enterprise Linux 10 · firefox.src as a component of Red Hat Enterprise Linux 10 · rhel10/firefox-flatpak as a component of Red Hat Enterprise Linux 10 · +20 more

Full record on NVD

Fix

  1. No fix available, says the vendor Red Hat Product Security CVE-2026-109740 · 17 productsAffected
  2. No fix planned, says the vendor Red Hat Product Security CVE-2026-109740 · 6 productsOut of support scope

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Published
2026-10-13
Last Modified
2026-10-19
NVD status
Deferred

Frequently asked questions

What is CVE-2026-109740?

Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.

Is CVE-2026-109740 actively exploited?

Active exploitation of CVE-2026-109740 has not been confirmed. Its EPSS score was 0.3% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-109740?

CVE-2026-109740 has a CVSS v3 base score of 9.6 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H.

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