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TI-2021-06308 Aliases CVE-2021-23987GHSA-5597-54m5-f56x

Out-of-bounds write in Mozilla Firefox ESR

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 and community members reported memory safety bugs present in Firefox 86 and Firefox ESR 78.8. 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 ESR < 78.9, Firefox < 87, and Thunderbird < 78.9.

Why it matters now

EPSS 0.01416 72nd percentileScored 2026-11-07
Fix Partial Firefox ESR (Mozilla): 78.9Firefox (Mozilla): 87+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
MozillaFirefox ESRbefore 78.978.9Patch availableCNA
MozillaFirefoxbefore 8787Patch availableCNA
MozillaThunderbirdbefore 78.978.9Patch availableCNA
  • Firefox ESR VendorMozilla Affected before 78.9 Fixed in 78.9 Patch available CNA
  • Firefox VendorMozilla Affected before 87 Fixed in 87 Patch available CNA
  • Thunderbird VendorMozilla Affected before 78.9 Fixed in 78.9 Patch available CNA

CPE configurations NVD · 3

CPEVersionsRoleVendor
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*before 87.0VulnerableMozilla
cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*before 78.9VulnerableMozilla
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*before 78.9VulnerableMozilla
  • cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* Versions before 87.0 Vulnerable ·Mozilla
  • cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:* Versions before 78.9 Vulnerable ·Mozilla
  • cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* Versions before 78.9 Vulnerable ·Mozilla

Remediation

  • Fix · CNA Firefox ESR (Mozilla) Fixed in 78.9
  • Fix · CNA Firefox (Mozilla) Fixed in 87
  • Fix · CNA Thunderbird (Mozilla) Fixed in 78.9

Red Hat 8 advisories

  • RHSA-2021:0992 Released 2021-03-25 · Red Hat rating Important
    firefox security update
    • Red Hat Enterprise Linux Client (v. 7) firefox-78.9.0-1.el7_9
    • Red Hat Enterprise Linux Client Optional (v. 7) firefox-78.9.0-1.el7_9
    • Red Hat Enterprise Linux Server (v. 7) firefox-78.9.0-1.el7_9
    • Red Hat Enterprise Linux Server Optional (v. 7) firefox-78.9.0-1.el7_9
    • Red Hat Enterprise Linux Workstation (v. 7) firefox-78.9.0-1.el7_9
    • Red Hat Enterprise Linux Workstation Optional (v. 7) firefox-78.9.0-1.el7_9
  • RHSA-2021:0996 Released 2021-03-25 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux Client (v. 7) thunderbird-78.9.0-3.el7_9
    • Red Hat Enterprise Linux Server Optional (v. 7) thunderbird-78.9.0-3.el7_9
    • Red Hat Enterprise Linux Workstation (v. 7) thunderbird-78.9.0-3.el7_9
  • RHSA-2021:0994 Released 2021-03-25 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird-78.9.0-3.el8_2
Show 5 more Red Hat advisories
  • RHSA-2021:0989 Released 2021-03-25 · Red Hat rating Important
    firefox security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.2) firefox-78.9.0-1.el8_2
  • RHSA-2021:0993 Released 2021-03-25 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream (v. 8) thunderbird-78.9.0-3.el8_3
  • RHSA-2021:0995 Released 2021-03-25 · Red Hat rating Important
    thunderbird security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.1) thunderbird-78.9.0-3.el8_1
  • RHSA-2021:0991 Released 2021-03-25 · Red Hat rating Important
    firefox security update
    • Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox-78.9.0-1.el8_1
  • RHSA-2021:0990 Released 2021-03-25 · Red Hat rating Important
    firefox security update
    • Red Hat Enterprise Linux AppStream (v. 8) firefox-78.9.0-1.el8_3

Fixed in the same release

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

  • Release ·

    Mozilla Firefox 87

    8 records Highest priority Priority MEDIUM 2 MEDIUM, 6 LOW

    Other records, highest priority first

    • TI-2021-06309 Out-of-bounds write in Mozilla FirefoxPriority MEDIUM 40
    • TI-2021-06302 Out-of-bounds write in Mozilla Firefox ESRPriority LOW 38
    • TI-2021-06306 If an attacker is able to alter specific about:config values (for example malware running…Priority LOW 32
    Show all 8 records →
  • Release ·

    Mozilla Firefox ESR, Thunderbird 78.9

    4 records Highest priority Priority MEDIUM 1 MEDIUM, 3 LOW

    Other records, highest priority first

    • TI-2021-06302 Out-of-bounds write in Mozilla Firefox ESRPriority LOW 38
    • TI-2021-06305 Authentication bypass by spoofing in Mozilla Firefox ESRPriority LOW 31
    • TI-2021-06303 Using techniques that built on the slipstream research, a malicious webpage could have…Priority LOW 30
    Show all 4 records →

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-2021:0990, RHSA-2021:0993
Red Hat Enterprise Linux AppStream EUS (v. 8.1)Fixed RHSA-2021:0991, RHSA-2021:0995
Red Hat Enterprise Linux AppStream EUS (v. 8.2)Fixed RHSA-2021:0989, RHSA-2021:0994
Red Hat Enterprise Linux Client (v. 7)Fixed RHSA-2021:0992, RHSA-2021:0996
Red Hat Enterprise Linux Client Optional (v. 7)Fixed RHSA-2021:0992
Red Hat Enterprise Linux Server (v. 7)Fixed RHSA-2021:0992
Red Hat Enterprise Linux Server Optional (v. 7)Fixed RHSA-2021:0992, RHSA-2021:0996
Red Hat Enterprise Linux Workstation (v. 7)Fixed RHSA-2021:0992, RHSA-2021:0996
Red Hat Enterprise Linux Workstation Optional (v. 7)Fixed RHSA-2021:0992

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-23987
  2. 2026-10-03 Alias added: GHSA-5597-54m5-f56x

References

Patch 1

Advisory 3

  • 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