CVE-2026-6786 — Out-of-bounds Read in Mozilla Firefox

CWE-125 — Out-of-bounds ReadCWE-416 — Use After FreeCWE-787 — Out-of-bounds Write7 documents4 sources
Severity
8.1HIGHNVD
EPSS
0.1%
top 80.36%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
3
Mozilla FirefoxMozilla Firefox ESRMozilla Thunderbird
Timeline
Latest updateApr 21
PublishedApr 26

Description

Memory safety bugs present in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149. 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 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HExploitability: 2.2 | Impact: 5.9

Affected Packages3 packages

▶Mozillamozilla/firefox< Firefox 150
▶Mozillamozilla/firefox_esr< Firefox ESR 140.10
▶Mozillamozilla/thunderbird< Thunderbird 140.10+1

📋Vendor Advisories

5
Red Hat
firefox: thunderbird: Memory safety bugs fixed in Firefox ESR 140.10, Thunderbird ESR 140.10, Firefox 150 and Thunderbird 150↗2026-04-21
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Mozilla
Mozilla Foundation Security Advisory 2026-34: CVE-2026-6786↗
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Mozilla
Mozilla Foundation Security Advisory 2026-32: CVE-2026-6786↗
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Mozilla
Mozilla Foundation Security Advisory 2026-33: CVE-2026-6786↗
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Mozilla
Mozilla Foundation Security Advisory 2026-30: CVE-2026-6786↗
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💬Community

1
Bugzilla
CVE-2026-6786 firefox: thunderbird: Memory safety bugs fixed in Firefox ESR 140.10, Thunderbird ESR 140.10, Firefox 150 and Thunderbird 150↗2026-04-21
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CVE-2026-6786 — Out-of-bounds Read in Mozilla Firefox | cvebase