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CVE-2026-84145

Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15

HIGH
7.5
CVSS Score
Published: September 1, 2026 at 12:18 PM UTC
Updated: September 3, 2026 at 01:04 PM UTC
2 products affected across 1 vendorFirefoxThunderbird

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Severity
HIGH7.5
Exploit prediction
EPSS 0.4%
SSVC
No known exploit

Description

Internally found bugs present in Firefox 154, Firefox ESR 153.1, Firefox ESR 140.14 and Firefox ESR 115.39. 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. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Firefox· Mozilla
95%
v < 115.40.0116.0 ≤ v < 140.15.0141.0.0 ≤ v < 153.2.0154.0.0 ≤ v < 155.0.0
Vendor states this is fixed in 115.40 (unaffected)
Affected range stops below 115.40.0, so it looks safe — our inference, not a vendor statement
Vendor states this is fixed in 140.15 (unaffected)
Affected range stops below 140.15.0, so it looks safe — our inference, not a vendor statement
Vendor states this is fixed in 153.2 (unaffected)
Affected range stops below 153.2.0, so it looks safe — our inference, not a vendor statement
Vendor states this is fixed in 155 (unaffected)
Affected range stops below 155.0.0, so it looks safe — our inference, not a vendor statement
Thunderbird· Mozilla
95%
v < 140.15.0141.0 ≤ v < 153.2.0154.0 ≤ v < 155.0
Vendor states this is fixed in 140.15 (unaffected)
Affected range stops below 140.15.0, so it looks safe — our inference, not a vendor statement
Vendor states this is fixed in 153.2 (unaffected)
Affected range stops below 153.2.0, so it looks safe — our inference, not a vendor statement
Vendor states this is fixed in 155 (unaffected)
Affected range stops below 155.0, so it looks safe — our inference, not a vendor statement

References (10)

Broken Link
Source: cverecord
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2054640%2C2054650%2C2054652%2C2055693%2C2055705%2C2058051%2C2058652%2C2058660%2C2059027%2C2061220%2C2061242%2C2061285%2C2061300%2C2061316%2C2061397
Broken Link
Source: cverecord
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2058001%2C2059139%2C2062400%2C2062419
Permissions Required
Source: cverecord
https://bugzilla.mozilla.org/show_bug.cgi?id=2055678
Vendor Advisory
Source: cverecord
https://www.mozilla.org/security/advisories/mfsa2026-82/
Vendor Advisory
Source: cverecord
https://www.mozilla.org/security/advisories/mfsa2026-83/
Vendor Advisory
Source: cverecord
https://www.mozilla.org/security/advisories/mfsa2026-84/
Vendor Advisory
Source: cverecord
https://www.mozilla.org/security/advisories/mfsa2026-85/
Vendor Advisory
Source: cverecord
https://www.mozilla.org/security/advisories/mfsa2026-86/

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.5HIGHCISA-ADP
Attack Vector
NETWORK
Complexity
HIGH
Privileges
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Vector?

Quick Info

StatusANALYZED
CWE
CWE-119

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