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Fencer Intel
medium 6.5

CVE-2021-38492 json

When delegating navigations to the operating system, Firefox would accept the `mk` scheme which might allow attackers to launch pages and e…

published 5y ago modified 4mo ago also EUVD-2021-24944

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 67%
public exploits
0
none known

Summary

When delegating navigations to the operating system, Firefox would accept the `mk` scheme which might allow attackers to launch pages and execute scripts in Internet Explorer in unprivileged mode. *This bug only affects Firefox for Windows. Other operating systems are unaffected.*. This vulnerability affects Firefox < 92, Thunderbird < 91.1, Thunderbird < 78.14, Firefox ESR < 78.14, and Firefox ESR < 91.1.

Patch / fix

  • Mozilla Firefox 92
  • Mozilla Thunderbird 78.14, 91.1
  • Mozilla Firefox ESR 78.14, 91.1
  • MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +11 more 91.9.0-112.104.1
  • MozillaFirefox SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +7 more 91.9.0-150000.150.34.1
  • MozillaThunderbird SLE Workstation Extension 15 SP3, SLE Workstation Extension 15 SP2 91.4.0-8.45.2
  • MozillaFirefox SLE Module for Desktop Applications 15 SP3, SLE Module for Desktop Applications 15 SP2 91.2.0-8.54.1
  • MozillaFirefox-branding-SLE SLE Module for Desktop Applications 15 SP3, SLE Module for Desktop Applications 15 SP2 91-9.5.1
  • MozillaFirefox SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +7 more 91.2.0-3.155.2
  • MozillaFirefox-branding-SLE SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +7 more 91-4.19.1
  • MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +11 more 91.1.0-112.71.1

suse advisories SUSE-SU-2022:1582-1SUSE-SU-2022:1577-1SUSE-SU-2021:4150-1SUSE-SU-2021:14826-1SUSE-SU-2021:3451-1SUSE-SU-2021:3331-1

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 92.0-1.2
  • MozillaThunderbird openSUSE Tumbleweed 91.1.1-1.1
  • MozillaThunderbird openSUSE Leap 15.2 91.4.0-lp152.2.52.1
  • MozillaThunderbird openSUSE Leap 15.3 91.4.0-8.45.2
  • MozillaFirefox openSUSE Leap 15.2 91.2.0-lp152.2.67.1
  • rust-cbindgen openSUSE Leap 15.2 0.19.0-lp152.2.7.1
  • MozillaFirefox openSUSE Leap 15.3 91.2.0-8.54.1

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1openSUSE-SU-2024:10601-1openSUSE-SU-2021:1635-1openSUSE-SU-2021:4150-1openSUSE-SU-2021:1367-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +6 more 92.0.1-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 92.0.1-r0
  • firefox-esr Alpine 3.14, Alpine 3.13 78.14.0-r0
  • firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +6 more 91.2.0-r0
  • thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 91.3.2-r0

alpine advisories ALPINE-CVE-2021-38492

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2021-38492 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-38492 updated cvss 6.1

Mozilla: Navigating to `mk:` URL scheme could load Internet Explorer

  • Red Hat Enterprise Linux 6 firefox, thunderbird Red Hat Enterprise Linux 7 firefox, thunderbird Red Hat Enterprise Linux 8 firefox, thunderbird
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.16% chance of exploitation in the next 30 days, higher than 67% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • bugzilla.mozilla.org https://bugzilla.mozilla.org/show_bug.cgi?id=1721107 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird
  • Mozilla Firefox ESR

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.