Uninitialized-memory use via malformed MIME error path
Published Sep 1, 2026 · Updated Sep 2, 2026
Uninitialized-memory use in Thunderbird before 155, ESR 153.2, and ESR 140.15 allows attackers to cause unspecified impact via crafted MIME bodies. The MIME parser enters an error path for certain body structures and then consumes memory that was never initialized. Mozilla states that ordinary email reading generally does not expose these flaws because Thunderbird disables scripting, leaving risk in browser-like contexts.
Summary
What happened
Uninitialized-memory use in Thunderbird before 155, ESR 153.2, and ESR 140.15 allows attackers to cause unspecified impact via crafted MIME bodies. The MIME parser enters an error path for certain body structures and then consumes memory that was never initialized. Mozilla states that ordinary email reading generally does not expose these flaws because Thunderbird disables scripting, leaving risk in browser-like contexts.
The record
- CVE
- CVE-2026-84639
- Published
- Sep 1, 2026
- Updated
- Sep 2, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- Unavailable
- Attack vector
- Unavailable
- Privileges
- Unavailable
Timeline
How it unfolded
- Sep 1, 2026CVE publishedPublication date reported by the CVE source.
- Sep 2, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
What conditions does exploitation require?
What is affected?
Affected products and versions are unavailable in this record.
Published CVSS scores
No CVSS assessment is available in this record.
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
No sourced classifications are available.
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo