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 and community members reported memory safety bugs present in Firefox 93 and Firefox ESR 91.2. 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 < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.
Why it matters now
EPSS 0.01248 69th percentileScored 2026-11-07
Fix Partial Firefox (Mozilla): 94Thunderbird (Mozilla): 91.3+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
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Mozilla | Firefox | before 94 | 94 | Patch available | CNA |
| Mozilla | Thunderbird | before 91.3 | 91.3 | Patch available | CNA |
| Mozilla | Firefox ESR | before 91.3 | 91.3 | Patch available | CNA |
- Firefox VendorMozilla Affected before 94 Fixed in 94 Patch available CNA
- Thunderbird VendorMozilla Affected before 91.3 Fixed in 91.3 Patch available CNA
- Firefox ESR VendorMozilla Affected before 91.3 Fixed in 91.3 Patch available CNA
CPE configurations NVD · 6
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* | before 94.0 | Vulnerable | Mozilla |
| cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:* | before 91.3.0 | Vulnerable | Mozilla |
| cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* | before 91.3.0 | Vulnerable | Mozilla |
| cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:* | 9.0 | Vulnerable | Debian |
| cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* | 10.0 | Vulnerable | Debian |
| cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:* | 11.0 | Vulnerable | Debian |
- cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* Versions before 94.0 Vulnerable ·Mozilla
- cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:* Versions before 91.3.0 Vulnerable ·Mozilla
- cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* Versions before 91.3.0 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
- cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:* Versions 11.0 Vulnerable ·Debian
Remediation
- Fix · CNA Firefox (Mozilla) Fixed in 94
- Fix · CNA Thunderbird (Mozilla) Fixed in 91.3
- Fix · CNA Firefox ESR (Mozilla) Fixed in 91.3
Red Hat 8 advisories
- RHSA-2021:4605 Released 2021-11-10 · Red Hat rating Importantfirefox security update
- Red Hat Enterprise Linux AppStream EUS (v. 8.2) firefox-91.3.0-1.el8_2
- RHSA-2021:4607 Released 2021-11-10 · Red Hat rating Importantfirefox security update
- Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox-91.3.0-1.el8_1
- RHSA-2021:4134 Released 2021-11-04 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux Client (v. 7) thunderbird-91.3.0-2.el7_9
- Red Hat Enterprise Linux Server Optional (v. 7) thunderbird-91.3.0-2.el7_9
- Red Hat Enterprise Linux Workstation (v. 7) thunderbird-91.3.0-2.el7_9
Show 5 more Red Hat advisories
- RHSA-2021:4130 Released 2021-11-04 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream (v. 8) thunderbird-91.3.0-2.el8_4
- RHSA-2021:4132 Released 2021-11-04 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird-91.3.0-2.el8_2
- RHSA-2021:4133 Released 2021-11-04 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream EUS (v. 8.1) thunderbird-91.3.0-2.el8_1
- RHSA-2021:4123 Released 2021-11-03 · Red Hat rating Importantfirefox security update
- Red Hat Enterprise Linux AppStream (v. 8) firefox-91.3.0-1.el8_4
- RHSA-2021:4116 Released 2021-11-03 · Red Hat rating Importantfirefox security update
- Red Hat Enterprise Linux Client (v. 7) firefox-91.3.0-1.el7_9
- Red Hat Enterprise Linux Client Optional (v. 7) firefox-91.3.0-1.el7_9
- Red Hat Enterprise Linux Server (v. 7) firefox-91.3.0-1.el7_9
- Red Hat Enterprise Linux Server Optional (v. 7) firefox-91.3.0-1.el7_9
- Red Hat Enterprise Linux Workstation (v. 7) firefox-91.3.0-1.el7_9
- Red Hat Enterprise Linux Workstation Optional (v. 7) firefox-91.3.0-1.el7_9
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 — DSA-5026
17 records Highest priority Priority MEDIUM 6 MEDIUM, 11 LOW
Other records, highest priority first
- TI-2021-16103 Incorrect authorization in Mozilla FirefoxPriority MEDIUM 50
- TI-2021-19429 Use after free in Mozilla ThunderbirdPriority MEDIUM 42
- TI-2021-19427 Incorrect type conversion in Mozilla ThunderbirdPriority MEDIUM 42
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux AppStream (v. 8) | Fixed | RHSA-2021:4123, RHSA-2021:4130 |
| Red Hat Enterprise Linux AppStream EUS (v. 8.1) | Fixed | RHSA-2021:4133, RHSA-2021:4607 |
| Red Hat Enterprise Linux AppStream EUS (v. 8.2) | Fixed | RHSA-2021:4132, RHSA-2021:4605 |
| Red Hat Enterprise Linux Client (v. 7) | Fixed | RHSA-2021:4116, RHSA-2021:4134 |
| Red Hat Enterprise Linux Client Optional (v. 7) | Fixed | RHSA-2021:4116 |
| Red Hat Enterprise Linux Server (v. 7) | Fixed | RHSA-2021:4116 |
| Red Hat Enterprise Linux Server Optional (v. 7) | Fixed | RHSA-2021:4116, RHSA-2021:4134 |
| Red Hat Enterprise Linux Workstation (v. 7) | Fixed | RHSA-2021:4116, RHSA-2021:4134 |
| Red Hat Enterprise Linux Workstation Optional (v. 7) | Fixed | RHSA-2021:4116 |
Timeline
- 2026-10-02 Threatist record created from CVE-2021-43534
- 2026-10-03 Alias added: GHSA-xcm8-pjqh-87pg
References
Advisory 8
- https://www.mozilla.org/security/advisories/mfsa2021-49/
- https://www.mozilla.org/security/advisories/mfsa2021-50/
- https://www.mozilla.org/security/advisories/mfsa2021-48/
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=1606864%2C1712671%2C1730048%2C1735152
- DSA-5026
- [debian-lts-announce] 20211229 [SECURITY] [DLA 2863-1] firefox-esr security update
- DSA-5034
- [debian-lts-announce] 20220104 [SECURITY] [DLA 2874-1] thunderbird security update
More Mozilla Firefox vulnerabilities
- 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
Sources
- CVE-2021-43534 · CVE Program
- CVE-2021-43534 · NVD
- FIRST EPSS
- GHSA-xcm8-pjqh-87pg · GitHub Advisory Database · CC BY 4.0
- CVE-2021-43534 · Red Hat security data · CC BY 4.0
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