CVE-2026-84142

Exploitation

Assessed, none found. CISA's assessment recorded neither public exploit code nor evidence of exploitation when it was made.

SSVC decision

• ExploitationnoneCISA recorded no public exploit code and no evidence of exploitation.
• AutomatableyesAn attacker can reliably automate reconnaissance through exploitation, so this scales.
• Technical ImpacttotalSuccessful exploitation gives total control of the vulnerable component.

CISA publishes the decision points, not a final SSVC decision. The decision also depends on mission and well-being impact, which is a property of your deployment rather than of the vulnerability.

EPSS probability

0.56% probability of exploitation activity in the next 30 days.

EPSS percentile

Equal to or higher than the score of 46.3% of scored records. A rank, not a probability.

NVD base score

9.8 (CVSS v3.x), scored by the NVD independently of the CNA.

NVD CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

NVD analysis status

Modified. NVD last modified this record on 2026-09-03.

Red Hat severity

Moderate. Red Hat's rating for its own products, not a CVSS rating.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

Published

2026-09-01 12:19Z1 MO AGO

Last updated

2026-09-03 17:23Z1 MO AGO

Reserved

2026-09-01

Assigning CNA

mozilla

Record state

PUBLISHED

Severity

Critical (CVSS 9.8)

CNA CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Weaknesses

• CWE-200Exposure of Sensitive Information to an Unauthorized ActorClass
• CWE-119Improper Restriction of Operations within the Bounds of a Memory BufferClass
• CWE-787Out-of-bounds WriteBase

Data version

5.2

Document digest

dbffac7fe30c769b45be9058b2cb27160ed338bed6e6f3a9337097df9e57c1b8

• bugzilla.mozilla.orgModerate Severity internally found bugs fixed in Thunderbird 155https://bugzilla.mozilla.org/buglist.cgi?bug_id=2029421%2C2040889%2C2045313%2C2045435%2C2053578%2C2058621%2C2058626
• bugzilla.mozilla.orgLow Severity internally found bugs fixed in Thunderbird 155https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048796%2C2053150%2C2057356
• www.mozilla.orghttps://www.mozilla.org/security/advisories/mfsa2026-82/
• www.mozilla.orghttps://www.mozilla.org/security/advisories/mfsa2026-86/