Read the docs
TI-2026-71679 Aliases CVE-2026-109763GHSA-gcff-5w52-74vw

Mozilla File Handling mitigation bypass fixed in Firefox and Thunderbird

Priority LOW 24CWE-20Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
Low · Low · None
Fix status
Partial Red Hat: 3 fixed, 4 without a fix

Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA and Red Hat.

Summary

Mozilla fixed a mitigation bypass in the File Handling component (CWE-20, Improper Input Validation) in Firefox 158, Firefox ESR 153.5, Thunderbird 158 and Thunderbird 153.5. The CVSS 3.1 base score is 5.4 (MEDIUM), and the vector requires user interaction and grants low confidentiality and integrity impact. CISA has not added the flaw to KEV, and the references contain no exploit link.

Written with Claude Haiku 5.5 from the sources below · 2026-11-06

Description from the CNA

Mitigation bypass in the File Handling component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00248 16th percentileScored 2026-11-07
Fix Partial Firefox (Mozilla): 153.5, 158Thunderbird (Mozilla): 153.5, 158Red Hat: 4 advisoriesRed Hat: 3 fixed, 4 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MozillaFirefox—153.5, 158Patch availableCNA
MozillaThunderbird—153.5, 158Patch availableCNA
  • Firefox VendorMozilla Affected — Fixed in 153.5, 158 Patch available CNA
  • Thunderbird VendorMozilla Affected — Fixed in 153.5, 158 Patch available CNA

CPE names Threatist (inferred) · 2

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*——Mozilla
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*——Mozilla
  • cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* Versions — — ·Mozilla
  • cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* Versions — — ·Mozilla

Remediation

Update Firefox to 158 or ESR 153.5 and Thunderbird to 158 or 153.5. Red Hat Enterprise Linux AppStream (v. 9), E4S (v.9.4) and EUS (v.9.6) have fixes through RHSA-2026:89757, RHSA-2026:93443, RHSA-2026:95597 and RHSA-2026:95596. Red Hat Enterprise Linux 6, 7, 8 and 10 have no fix available, and Red Hat plans no fix for RHEL 6.

Written with Claude Haiku 5.5 from the sources below · 2026-11-06

  • Fix · CNA Firefox (Mozilla) Fixed in 153.5, 158
  • Fix · CNA Thunderbird (Mozilla) Fixed in 153.5, 158

Red Hat 4 advisories

  • RHSA-2026:95596 Released 2026-11-05 · Red Hat rating Important
    thunderbird security, bug fix, and enhancement update
    • Red Hat Enterprise Linux AppStream EUS (v.9.6) thunderbird-153.5.0-1.el9_6
  • RHSA-2026:95597 Released 2026-11-05 · Red Hat rating Important
    thunderbird security, bug fix, and enhancement update
    • Red Hat Enterprise Linux AppStream E4S (v.9.4) thunderbird-153.5.0-1.el9_4
  • RHSA-2026:93443 Released 2026-11-02 · Red Hat rating Important
    thunderbird security, bug fix, and enhancement update
    • Red Hat Enterprise Linux AppStream (v. 9) thunderbird-153.5.0-1.el9_8
Show 1 more Red Hat advisories
  • RHSA-2026:89757 Released 2026-10-26 · Red Hat rating Important
    firefox security, bug fix, and enhancement update
    • Red Hat Enterprise Linux AppStream (v. 9) firefox-153.5.0-1.el9_8, firefox-x11-153.5.0-1.el9_8

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Enterprise Linux 10AffectedNo fix yet
Red Hat Enterprise Linux 6AffectedNo fix planned: Out of support scope
Red Hat Enterprise Linux 7AffectedNo fix yet
Red Hat Enterprise Linux 8AffectedNo fix yet
Red Hat Enterprise Linux AppStream (v. 9)Fixed RHSA-2026:89757, RHSA-2026:93443
Red Hat Enterprise Linux AppStream E4S (v.9.4)Fixed RHSA-2026:95597
Red Hat Enterprise Linux AppStream EUS (v.9.6)Fixed RHSA-2026:95596

Timeline

  1. 2026-10-13 Threatist record created from CVE-2026-109763
  2. 2026-10-13 Alias added: GHSA-gcff-5w52-74vw
  3. 2026-10-13 Fix available: Mozilla/[email protected], Mozilla/Thunderbird@158 · CNA
  4. 2026-10-13 2 new references · CNA
  5. 2026-10-30 CVSS score added · CISA ADP
  6. 2026-10-30 Weakness changed · CISA ADP
  7. 2026-10-30 CISA SSVC decision points changed
  8. 2026-10-31 Affected versions changed · Red Hat
  9. 2026-10-31 CVSS score added · Red Hat
  10. 2026-10-31 Fix available: RHSA-2026:89757 · Red Hat
  11. 2026-10-31 Fix available: Red Hat Enterprise Linux AppStream (v. 9) · Red Hat
  12. 2026-11-02 Fix available: RHSA-2026:93443 · Red Hat
  13. 2026-11-02 Affected versions changed · Red Hat
  14. 2026-11-06 Fix available: RHSA-2026:95597 · Red Hat
  15. 2026-11-06 Fix available: Red Hat Enterprise Linux AppStream E4S (v.9.4), Red Hat Enterprise Linux AppStream EUS (v.9.6) · Red Hat
  16. 2026-11-06 Fix available: RHSA-2026:95596 · Red Hat

References

Other 5

  • TI-2024-08981 Use after free in Mozilla Firefox KEVCVSS 3.1CRITICAL 9.8
  • TI-2022-09832 Use after free in Mozilla Firefox KEVCVSS 3.1CRITICAL 9.6
  • TI-2019-08769 Improper input validation in Mozilla Firefox ESR KEVCVSS 3.1CRITICAL 10.0
  • TI-2010-03577 Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before… KEVCVSS 3.1CRITICAL 9.8
  • TI-2023-04799 Out-of-bounds write in Google Chrome KEVCVSS 3.1HIGH 8.8
  • TI-2023-04477 Out-of-bounds write in Google Chrome KEVCVSS 3.1HIGH 8.8
See all 4204 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences