High [CVE-2026-74990] Internally found bugs fixed in Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154
This high-severity Red Hat Linux advisory covers CVE-2026-74990 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7.
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Summary
A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: Internally found bugs present in Thunderbird ESR 140.13, Thunderbird ESR 153.0 and Thunderbird 153.
Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.
Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H). Weakness: CWE-787.
Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9. Will not fix / out of support: Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7.
Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Red Hat package: firefox; Red Hat package: thunderbird.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 1 hour ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 1 hour ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 1 hour ago·verify at source
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