High 8.1Published Apr 7, 2026

CVE-2026-5734Memory safety bugs fixed in Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2

Updated under an hour ago (Oct 26, 2026, 7:10 PM ET)

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It affects Mozilla Firefox and 9 other products. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 was fixed in Firefox 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

CVSS: 8.1 HIGH (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-120, CWE-787
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: mozilla
NVD analysis: Modified
Record last updated: Jul 14, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Mozilla Firefox mozilla:firefox (from the name)	140.9.1 builds before 140.* not affected; from 149.0.2 not affected	CNA record
Mozilla Thunderbird mozilla:thunderbird (from the name)	140.9.1 builds before 140.* not affected; from 149.0.2 not affected	CNA record
Red Hat Red Hat Enterprise Linux 10 redhat:enterprise_linux	from 0:140.9.1-1.el10_1 not affected	CISA ADP
Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support redhat:enterprise_linux_eus	from 0:140.9.1-1.el10_0 not affected	CISA ADP
Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support redhat:rhel_els	from 0:140.9.1-2.el7_9 not affected	CISA ADP
Red Hat Red Hat Enterprise Linux 8.2 Advanced Update Support redhat:rhel_aus	from 0:140.9.1-1.el8_2 not affected	CISA ADP
Red Hat Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On redhat:rhel_eus_long_life	from 0:140.9.1-1.el8_4 not affected	CISA ADP
Red Hat Red Hat Enterprise Linux 8.6 Telecommunications Update Service redhat:rhel_tus	from 0:140.9.1-1.el8_6 not affected	CISA ADP
Red Hat Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions redhat:rhel_e4s	from 0:140.9.1-1.el8_6 not affected	CISA ADP
Red Hat Red Hat Enterprise Linux 9.4 Extended Update Support redhat:rhel_eus	from 0:140.9.1-1.el9_4 not affected	CISA ADP
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References

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=2022369%2C2023026%2C2023545%2C2023555%2C2023958%2C2025422%2C2025468%2C2025492%2C2025505	broken-link, issue-tracking
https://www.mozilla.org/security/advisories/mfsa2026-25/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-27/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-28/
https://www.mozilla.org/security/advisories/mfsa2026-29/
https://access.redhat.com/errata/RHSA-2026:11805
https://access.redhat.com/errata/RHSA-2026:11813
https://access.redhat.com/errata/RHSA-2026:12264
https://access.redhat.com/errata/RHSA-2026:13342
https://access.redhat.com/errata/RHSA-2026:13412
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The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.