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CVE-2026-6763· NVD / CVE Program· CNA mozilla

Mitigation bypass in the File Handling component

Noroxi assessment

Priority: Monitor (action score 26/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.32% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: firefox (AlmaLinux:10) 140.10.0-1.el10_1; thunderbird (AlmaLinux:10) 140.10.0-1.el10_1.alma.1; firefox (AlmaLinux:8) 140.10.0-1.el8_10.alma.1.

Low priority for now. Upgrade to firefox (AlmaLinux:10) 140.10.0-1.el10_1; thunderbird (AlmaLinux:10) 140.10.0-1.el10_1.alma.1; firefox (AlmaLinux:8) 140.10.0-1.el8_10.alma.1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Mitigation bypass in the File Handling component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

MediumCVSS 6.5 · v3.1—No exploit Fix available
Published
Apr 21, 2026
Updated
Jun 17, 2026
EPSS
0.3% · 23th percentile

Report tools

JSON

Action score

26

Monitor

Low priority for now.

CVSS
26 / 40 · 6.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-6763

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
mozillafirefox
mozillathunderbird

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • mozilla firefoxbefore 140.10.0
  • mozilla firefoxbefore 150.0
  • mozilla thunderbird140.0 and later · before 140.10.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (mozilla). Independent of NVD's CPE analysis and usually ahead of it.

  • Mozilla Firefox

    • 140.10 and later · up to and including 140.*not affected · rpm
    • 150 and laternot affected · rpm

  • Mozilla Thunderbird

    • 140.10 and later · up to and including 140.*not affected · rpm
    • 150 and laternot affected · rpm

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:10firefoxbefore 140.10.0-1.el10_1140.10.0-1.el10_1
AlmaLinux:10thunderbirdbefore 140.10.0-1.el10_1.alma.1140.10.0-1.el10_1.alma.1
AlmaLinux:8firefoxbefore 140.10.0-1.el8_10.alma.1140.10.0-1.el8_10.alma.1
AlmaLinux:8thunderbirdbefore 140.10.0-1.el8_10.alma.1140.10.0-1.el8_10.alma.1
AlmaLinux:9firefoxbefore 140.10.0-1.el9_7.alma.1140.10.0-1.el9_7.alma.1
AlmaLinux:9firefox-x11before 140.10.0-1.el9_7.alma.1140.10.0-1.el9_7.alma.1
AlmaLinux:9thunderbirdbefore 140.10.1-1.el9_8.alma.1140.10.1-1.el9_8.alma.1
AlmaLinux:9thunderbirdbefore 140.10.0-1.el9_7.alma.1140.10.0-1.el9_7.alma.1
Debian:12firefox-esrbefore 140.10.0esr-1~deb12u1140.10.0esr-1~deb12u1
Debian:12thunderbirdbefore 1:140.10.0esr-1~deb12u11:140.10.0esr-1~deb12u1
Debian:13firefox-esrbefore 140.10.0esr-1~deb13u1140.10.0esr-1~deb13u1
Debian:13thunderbirdbefore 1:140.10.0esr-1~deb13u11:140.10.0esr-1~deb13u1
Debian:14firefox-esrbefore 140.10.0esr-1140.10.0esr-1
Debian:14thunderbirdbefore 1:140.10.0esr-11:140.10.0esr-1
openSUSE:TumbleweedMozillaFirefoxbefore 150.0-1.1150.0-1.1
openSUSE:TumbleweedMozillaThunderbirdbefore 140.9.1-1.1140.9.1-1.1
Red Hat:enterprise_linux_eus:10.0firefoxbefore 0:140.10.0-1.el10_00:140.10.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0firefox-debuginfobefore 0:140.10.0-1.el10_00:140.10.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0firefox-debugsourcebefore 0:140.10.0-1.el10_00:140.10.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0thunderbirdbefore 0:140.10.0-1.el10_00:140.10.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0thunderbird-debuginfobefore 0:140.10.0-1.el10_00:140.10.0-1.el10_0
Red Hat:enterprise_linux_eus:10.0thunderbird-debugsourcebefore 0:140.10.0-1.el10_00:140.10.0-1.el10_0
Red Hat:enterprise_linux:10.1firefoxbefore 0:140.10.0-1.el10_10:140.10.0-1.el10_1
Red Hat:enterprise_linux:10.1firefox-debuginfobefore 0:140.10.0-1.el10_10:140.10.0-1.el10_1

+84

Same product

mozilla: all records

Other highest-scoring records for the same primary product.

  • CVE-2010-3765Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x befKEV
    94Now
  • CVE-2019-11708Insufficient vetting of parameters passed with the Prompt:Open IPC message between child and parent processes can result in the non-sandboxeKEV
    87Now
  • CVE-2015-4495The PDF reader in Mozilla Firefox before 39.0.3, Firefox ESR 38.x before 38.1.1, and Firefox OS before 2.2 allows remote attackers to bypassKEV
    86Now

Published before and after this one in the same product

  • ← EarlierCVE-2026-6761Apr 21, 2026 · Privilege escalation in the Networking component
    35Monitor
  • ← EarlierCVE-2026-6762Apr 21, 2026 · Spoofing issue in the DOM: Core & HTML component
    25Monitor
  • Later →CVE-2026-6764Apr 21, 2026 · Incorrect boundary conditions in the DOM: Device Interfaces component
    26Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:firefox140.10.0-1.el9_7.alma.1 · AlmaLinux:9Package registry (OSV)
almalinux:firefox-x11140.10.0-1.el9_7.alma.1 · AlmaLinux:9Package registry (OSV)
almalinux:thunderbird140.10.0-1.el10_1.alma.1 · AlmaLinux:10Package registry (OSV)
debian:firefox-esr140.10.0esr-1~deb12u1 · Debian:12Package registry (OSV)
debian:thunderbird1:140.10.0esr-1~deb12u1 · Debian:12Package registry (OSV)
opensuse:MozillaFirefox150.0-1.1 · openSUSE:TumbleweedPackage registry (OSV)
opensuse:MozillaThunderbird140.9.1-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:firefox0:140.10.0-1.el9_7 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:firefox-debuginfo0:140.10.0-1.el9_7 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:firefox-debugsource0:140.10.0-1.el9_7 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:firefox-x110:140.10.0-1.el9_7 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:thunderbird0:140.10.0-1.el10_1 · Red Hat:enterprise_linux:10.1Package registry (OSV)
red hat:thunderbird-debuginfo0:140.10.0-1.el10_1 · Red Hat:enterprise_linux:10.1Package registry (OSV)
red hat:thunderbird-debugsource0:140.10.0-1.el10_1 · Red Hat:enterprise_linux:10.1Package registry (OSV)
rocky linux:firefox0:140.10.0-1.el9_7 · Rocky Linux:9Package registry (OSV)
rocky linux:thunderbird0:140.10.0-1.el10_1 · Rocky Linux:10Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-276156 days apartSandbox escape in the Graphics: WebRender component
    40Plan
  • CVE-2026-75874119 days apartSandbox escape in the Remote Settings Client component
    40Plan
  • CVE-2026-840121 days apartSandbox escape in the Profile Backup component
    39Monitor
  • CVE-2026-1637791 days apartMitigation bypass in the PDF Viewer component
    39Monitor
  • CVE-2026-1638291 days apartMitigation bypass in the DOM: Service Workers component
    39Monitor
  • CVE-2026-1638391 days apartMitigation bypass in the DOM: Networking component
    39Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
low · data can be read
Integrity
low · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
Low
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-693 · Protection Mechanism Failure

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records