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TI-2021-06299 Aliases CVE-2021-23978GHSA-3rjx-v36w-2rw5

Out-of-bounds write in Mozilla Firefox

Priority MEDIUM 41CWE-787Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
Code execution
Confidentiality · integrity · availability
High · High · High
Fix status
Partial Red Hat: 9 fixed, 1 without a fix

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat. Impact type from CWE-787 and the CVSS impact.

Summary

Mozilla developers reported memory safety bugs present in Firefox 85 and Firefox ESR 78.7. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 86, Thunderbird < 78.8, and Firefox ESR < 78.8.

Why it matters now

EPSS 0.0153 74th percentileScored 2026-11-07
Fix Partial Firefox (Mozilla): 86Thunderbird (Mozilla): 78.8+1 more productRed Hat: 8 advisoriesRed Hat: 9 fixed, 1 without a fix

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
MozillaFirefoxbefore 8686Patch availableCNA
MozillaThunderbirdbefore 78.878.8Patch availableCNA
MozillaFirefox ESRbefore 78.878.8Patch availableCNA
  • Firefox VendorMozilla Affected before 86 Fixed in 86 Patch available CNA
  • Thunderbird VendorMozilla Affected before 78.8 Fixed in 78.8 Patch available CNA
  • Firefox ESR VendorMozilla Affected before 78.8 Fixed in 78.8 Patch available CNA

CPE configurations NVD · 5

CPEVersionsRoleVendor
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*before 86.0VulnerableMozilla
cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*before 78.8VulnerableMozilla
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*before 78.8VulnerableMozilla
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*9.0VulnerableDebian
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*10.0VulnerableDebian
  • cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* Versions before 86.0 Vulnerable ·Mozilla
  • cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:* Versions before 78.8 Vulnerable ·Mozilla
  • cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* Versions before 78.8 Vulnerable ·Mozilla
  • cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:* Versions 9.0 Vulnerable ·Debian
  • cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* Versions 10.0 Vulnerable ·Debian

Remediation

  • Fix · CNA Firefox (Mozilla) Fixed in 86
  • Fix · CNA Thunderbird (Mozilla) Fixed in 78.8
  • Fix · CNA Firefox ESR (Mozilla) Fixed in 78.8

Red Hat 8 advisories

  • RHSA-2021:0661 Released 2021-02-24 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux Client (v. 7) thunderbird-78.8.0-1.el7_9
    • Red Hat Enterprise Linux Server Optional (v. 7) thunderbird-78.8.0-1.el7_9
    • Red Hat Enterprise Linux Workstation (v. 7) thunderbird-78.8.0-1.el7_9
  • RHSA-2021:0656 Released 2021-02-24 · Red Hat rating Critical
    firefox security update
    • Red Hat Enterprise Linux Client (v. 7) firefox-78.8.0-1.el7_9
    • Red Hat Enterprise Linux Client Optional (v. 7) firefox-78.8.0-1.el7_9
    • Red Hat Enterprise Linux Server (v. 7) firefox-78.8.0-1.el7_9
    • Red Hat Enterprise Linux Server Optional (v. 7) firefox-78.8.0-1.el7_9
    • Red Hat Enterprise Linux Workstation (v. 7) firefox-78.8.0-1.el7_9
    • Red Hat Enterprise Linux Workstation Optional (v. 7) firefox-78.8.0-1.el7_9
  • RHSA-2021:0662 Released 2021-02-24 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird-78.8.0-1.el8_2
Show 5 more Red Hat advisories
  • RHSA-2021:0660 Released 2021-02-24 · Red Hat rating Critical
    firefox security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.2) firefox-78.8.0-1.el8_2
  • RHSA-2021:0658 Released 2021-02-24 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.1) thunderbird-78.8.0-1.el8_1
  • RHSA-2021:0657 Released 2021-02-24 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream (v. 8) thunderbird-78.8.0-1.el8_3
  • RHSA-2021:0659 Released 2021-02-24 · Red Hat rating Critical
    firefox security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox-78.8.0-1.el8_1
  • RHSA-2021:0655 Released 2021-02-24 · Red Hat rating Critical
    firefox security update
    • Red Hat Enterprise Linux AppStream (v. 8) firefox-78.8.0-1.el8_3

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Advisory ·

    Mozilla Firefox, Firefox ESR, Thunderbird — GLSA-202104-10

    12 records Highest priority Priority MEDIUM 2 MEDIUM, 10 LOW

    Other records, highest priority first

    • TI-2021-06293 One phishing tactic on the web is to provide a link with HTTP Auth.Priority MEDIUM 40
    • TI-2021-06297 Clickjacking in Mozilla FirefoxPriority LOW 37
    • TI-2021-06284 Further techniques that built on the slipstream research combined with a malicious…Priority LOW 35
    Show all 12 records → Advisory →
  • Advisory ·

    Mozilla Firefox, Firefox ESR, Thunderbird — GLSA-202104-09

    5 records Highest priority Priority MEDIUM 1 MEDIUM, 4 LOW

    Other records, highest priority first

    • TI-2021-06284 Further techniques that built on the slipstream research combined with a malicious…Priority LOW 35
    • TI-2021-06294 Information disclosure through error messages in Mozilla FirefoxPriority LOW 32
    • TI-2021-06289 Information disclosure through error messages in Mozilla FirefoxPriority LOW 23
    Show all 5 records → Advisory →
Show 1 more group
  • Advisory ·

    Mozilla Firefox, Firefox ESR, Thunderbird — DSA-4866

    4 records Highest priority Priority MEDIUM 1 MEDIUM, 3 LOW

    Other records, highest priority first

    • TI-2021-06294 Information disclosure through error messages in Mozilla FirefoxPriority LOW 32
    • TI-2021-06289 Information disclosure through error messages in Mozilla FirefoxPriority LOW 23
    • TI-2021-06290 As specified in the W3C Content Security Policy draft, when creating a violation report…Priority LOW 22
    Show all 4 records → Advisory →

Vendor assessments

Red Hat

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

ProductStatusPlan or fix
Red Hat Enterprise Linux 6AffectedNo fix planned: Out of support scope
Red Hat Enterprise Linux AppStream (v. 8)Fixed RHSA-2021:0655, RHSA-2021:0657
Red Hat Enterprise Linux AppStream EUS (v. 8.1)Fixed RHSA-2021:0658, RHSA-2021:0659
Red Hat Enterprise Linux AppStream EUS (v. 8.2)Fixed RHSA-2021:0660, RHSA-2021:0662
Red Hat Enterprise Linux Client (v. 7)Fixed RHSA-2021:0656, RHSA-2021:0661
Red Hat Enterprise Linux Client Optional (v. 7)Fixed RHSA-2021:0656
Red Hat Enterprise Linux Server (v. 7)Fixed RHSA-2021:0656
Red Hat Enterprise Linux Server Optional (v. 7)Fixed RHSA-2021:0656, RHSA-2021:0661
Red Hat Enterprise Linux Workstation (v. 7)Fixed RHSA-2021:0656, RHSA-2021:0661
Red Hat Enterprise Linux Workstation Optional (v. 7)Fixed RHSA-2021:0656

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-23978
  2. 2026-10-03 Alias added: GHSA-3rjx-v36w-2rw5

References

Advisory 8

  • 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 3444 →

Sources

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