CVE-2026-84640
published 2026-09-01CVE-2026-84640: A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird…
PriorityP340high7.5CVSS 3.1
AVNACLPRNUINSUCHINAN
EPSS
0.26%
16.9th percentile
A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
Affected
8 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| mozilla | thunderbird | < Thunderbird 153.2 | Thunderbird 153.2 |
| mozilla | thunderbird | < Thunderbird 140.15 | Thunderbird 140.15 |
| mozilla | thunderbird | < Thunderbird 155 | Thunderbird 155 |
| mozilla | thunderbird | < 140.15.0 | 140.15.0 |
| mozilla | thunderbird | — | — |
| mozilla | thunderbird | >= 141.0 < 153.2.0 | 153.2.0 |
| mozilla | thunderbird | >= 154.0 < 155.0 | 155.0 |
| rhel10 | thunderbird-flatpak | — | — |
CVSS provenance
nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
vendor_redhat7.5HIGH
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Red Hat
thunderbird: One byte overflow read in mail parser
vendor_redhat·2026-09-01·CVSS 7.5
CVE-2026-84640 [HIGH] CWE-125 thunderbird: One byte overflow read in mail parser
thunderbird: One byte overflow read in mail parser
A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
A flaw was found in Thunderbird. A remote attacker could exploit this vulnerability by sending a maliciously constructed mail header. This could lead to a one-byte read past the end of a buffer, potentially resulting in information disclosure or other unpredictable behavior.
Statement: Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.
Package: rhel10/thunderbird-flatpak (Red Hat Enterprise Linux 10) - Affected
Package: thunderbird (Red Hat Enterprise Linux 10) - Affected
Package: thunde
Mozilla
Mozilla Foundation Security Advisory 2026-88: CVE-2026-84640
vendor_mozilla
CVE-2026-84640 Mozilla Foundation Security Advisory 2026-88: CVE-2026-84640
Mozilla Foundation Security Advisory 2026-88
CVE: CVE-2026-84640
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 153.2
Mozilla
Mozilla Foundation Security Advisory 2026-87: CVE-2026-84640
vendor_mozilla
CVE-2026-84640 Mozilla Foundation Security Advisory 2026-87: CVE-2026-84640
Mozilla Foundation Security Advisory 2026-87
CVE: CVE-2026-84640
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 140.15
Mozilla
Mozilla Foundation Security Advisory 2026-86: CVE-2026-84640
vendor_mozilla
CVE-2026-84640 Mozilla Foundation Security Advisory 2026-86: CVE-2026-84640
Mozilla Foundation Security Advisory 2026-86
CVE: CVE-2026-84640
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 155
GHSA
A maliciously constructed mail header could lead to a one byte read past the end of a buffer.
ghsa_unreviewed·2026-09-02
CVE-2026-84640 A maliciously constructed mail header could lead to a one byte read past the end of a buffer.
A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
VulDB
Mozilla Thunderbird up to 140.14/153.1/154 out-of-bounds (EUVD-2026-69709)
vuldb·2026-09-01
CVE-2026-84640 [CRITICAL] Mozilla Thunderbird up to 140.14/153.1/154 out-of-bounds (EUVD-2026-69709)
A vulnerability has been found in Mozilla Thunderbird up to 140.14/153.1/154 and classified as critical. This vulnerability affects unknown code. This manipulation causes out-of-bounds read.
The identification of this vulnerability is CVE-2026-84640. It is possible to initiate the attack remotely. There is no exploit available.
The affected component should be upgraded.
No detection rules found.
No public exploits indexed.
2026-09-01
Published