Skip to content
Noroxi
CVE-2020-26953· NVD / CVE Program· CNA mozilla

It was possible to cause the browser to enter fullscreen mode without displaying the security UI; thus making it possible to attempt a phish

Noroxi assessment

Priority: Monitor (action score 17/100)

  • 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: 1.2% (FIRST EPSS); higher than 69.8% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
  • Fixed version: firefox-esr (Debian:10) 78.5.0esr-1~deb10u1; thunderbird (Debian:10) 1:78.5.0-1~deb10u1; firefox-esr (Debian:12) 78.5.0esr-1.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to firefox-esr (Debian:10) 78.5.0esr-1~deb10u1; thunderbird (Debian:10) 1:78.5.0-1~deb10u1; firefox-esr (Debian:12) 78.5.0esr-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

It was possible to cause the browser to enter fullscreen mode without displaying the security UI; thus making it possible to attempt a phishing attack or otherwise confuse the user. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

MediumCVSS 4.3 · v3.1—No exploit Fix available
Published
Dec 8, 2020
Updated
Jun 16, 2026
EPSS
1.2% · 69th percentile

Report tools

JSON

Action score

17

Monitor

Low priority for now.

CVSS
17 / 40 · 4.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 1.2%

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-2020-26953

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

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits instantly.

Your free account also gets you

Running WordPress? Scan your site free with WP Lens

  • Stack alerts: add the products and versions you run, get the new CVEs that affect them
  • Uptime monitoring: 1 site, instant email when it goes down
  • Add your domain: subdomains and takeover risk scanned every week (1 domain)
  • 10 scans an hour on the security tools (3 a day without an account), an API key and MCP
  • All your scans in one panel: findings, what changed in the last scan, a report per domain or per client (PDF, share link)
All free tools

Sign up with email · Have an account? Sign in

Free account, no card. Unfollow any time.

Don't want an account? Get "Exploited this week" by email every MondayDon't want an account? RSS feed for mozilla records

Running WordPress? Scan your site free with WP Lens

Is your version affected? Check it

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.

We use this product, ask for help

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
mozillafirefox esr
mozillathunderbird

Do you have framing protection?

Clickjacking protection needs CSP frame-ancestors or X-Frame-Options. Check for free whether your site sends them.

Check security headers

Affected versions

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

  • mozilla firefoxbefore 83.0
  • mozilla firefox esrbefore 78.5
  • mozilla thunderbirdbefore 78.5

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

    • < 83affected

  • Mozilla Firefox ESR

    • < 78.5affected

  • Mozilla Thunderbird

    • < 78.5affected

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:10firefox-esrbefore 78.5.0esr-1~deb10u178.5.0esr-1~deb10u1
Debian:10thunderbirdbefore 1:78.5.0-1~deb10u11:78.5.0-1~deb10u1
Debian:12firefox-esrbefore 78.5.0esr-178.5.0esr-1
Debian:12thunderbirdbefore 1:78.5.0-11:78.5.0-1
Debian:9firefox-esrbefore 78.5.0esr-1~deb9u178.5.0esr-1~deb9u1
Debian:9thunderbirdbefore 1:78.5.0-1~deb9u11:78.5.0-1~deb9u1
openSUSE:Leap 15.1MozillaFirefoxbefore 78.5.0-lp151.2.79.178.5.0-lp151.2.79.1
openSUSE:Leap 15.1MozillaThunderbirdbefore 78.5.0-lp151.2.59.178.5.0-lp151.2.59.1
openSUSE:Leap 15.2MozillaFirefoxbefore 78.5.0-lp152.2.33.178.5.0-lp152.2.33.1
openSUSE:Leap 15.2MozillaFirefoxbefore 78.5.0-lp152.2.30.178.5.0-lp152.2.30.1
openSUSE:Leap 15.2MozillaThunderbirdbefore 78.5.0-lp152.2.19.178.5.0-lp152.2.19.1
Red Hat:enterprise_linux:6::clientfirefoxbefore 0:78.5.0-1.el6_100:78.5.0-1.el6_10
Red Hat:enterprise_linux:6::clientfirefox-debuginfobefore 0:78.5.0-1.el6_100:78.5.0-1.el6_10
Red Hat:enterprise_linux:6::clientthunderbirdbefore 0:78.5.0-1.el6_100:78.5.0-1.el6_10
Red Hat:enterprise_linux:6::clientthunderbird-debuginfobefore 0:78.5.0-1.el6_100:78.5.0-1.el6_10
Red Hat:enterprise_linux:7::clientfirefoxbefore 0:78.5.0-1.el7_90:78.5.0-1.el7_9
Red Hat:enterprise_linux:7::clientfirefox-debuginfobefore 0:78.5.0-1.el7_90:78.5.0-1.el7_9
Red Hat:enterprise_linux:7::clientthunderbirdbefore 0:78.5.0-1.el7_90:78.5.0-1.el7_9
Red Hat:enterprise_linux:7::clientthunderbird-debuginfobefore 0:78.5.0-1.el7_90:78.5.0-1.el7_9
Red Hat:enterprise_linux:8::appstreamfirefoxbefore 0:78.5.0-1.el8_30:78.5.0-1.el8_3
Red Hat:enterprise_linux:8::appstreamfirefox-debuginfobefore 0:78.5.0-1.el8_30:78.5.0-1.el8_3
Red Hat:enterprise_linux:8::appstreamfirefox-debugsourcebefore 0:78.5.0-1.el8_30:78.5.0-1.el8_3
Red Hat:enterprise_linux:8::appstreamthunderbirdbefore 0:78.5.0-1.el8_30:78.5.0-1.el8_3
Red Hat:enterprise_linux:8::appstreamthunderbird-debuginfobefore 0:78.5.0-1.el8_30:78.5.0-1.el8_3

+24

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-2020-26951Dec 8, 2020 · A parsing and event loading mismatch in Firefox's SVG code could have allowed load events to fire, even after sanitization.
    24Monitor
  • ← EarlierCVE-2020-26952Dec 8, 2020 · Incorrect bookkeeping of functions inlined during JIT compilation could have led to memory corruption and a potentially exploitable crash wh
    35Monitor
  • Later →CVE-2020-26956Dec 8, 2020 · In some cases, removing HTML elements during sanitization would keep existing SVG event handlers and therefore lead to XSS.
    24Monitor

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
debian:firefox-esr78.5.0esr-1 · Debian:12Package registry (OSV)
debian:thunderbird1:78.5.0-1 · Debian:12Package registry (OSV)
opensuse:MozillaFirefox78.5.0-lp152.2.30.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:MozillaThunderbird78.5.0-lp152.2.19.1 · openSUSE:Leap 15.2Package registry (OSV)
red hat:firefox0:78.5.0-1.el8_1 · Red Hat:rhel_eus:8.1::appstreamPackage registry (OSV)
red hat:firefox-debuginfo0:78.5.0-1.el8_1 · Red Hat:rhel_eus:8.1::appstreamPackage registry (OSV)
red hat:firefox-debugsource0:78.5.0-1.el8_1 · Red Hat:rhel_eus:8.1::appstreamPackage registry (OSV)
red hat:thunderbird0:78.5.0-1.el8_1 · Red Hat:rhel_eus:8.1::appstreamPackage registry (OSV)
red hat:thunderbird-debuginfo0:78.5.0-1.el8_1 · Red Hat:rhel_eus:8.1::appstreamPackage registry (OSV)
red hat:thunderbird-debugsource0:78.5.0-1.el8_1 · Red Hat:rhel_eus:8.1::appstreamPackage registry (OSV)
suse:MozillaFirefox78.5.0-78.105.1 · SUSE:Linux Enterprise Server 11 SP4-LTSSPackage registry (OSV)
suse:MozillaThunderbird78.5.0-3.107.1 · SUSE:Linux Enterprise Workstation Extension 15 SP1Package 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.

No credits in the CNA record.

Variant candidates

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

No nightly-computed relations.

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).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • A user must open a link or visit a page.
  • No special conditions are required; it is repeatable.

If successful

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

Weakness class (CWE)

CWE-1021 · Improper Restriction of Rendered UI Layers or Frames

CVSS vector

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

nvd-primary

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 (3 more)

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

All records