CVE-2026-103500: mozilla thunderbird Out-of-bounds Write
CVSS: 6.3v3.1MediumModified
AliasesUBUNTU-CVE-2026-103500DEBIAN-CVE-2026-103500
Published 30-09-2026Last modified 16-10-2026
Vulnerability summary
CVE-2026-103500 is a medium (CVSS 6.3) Out-of-bounds Write vulnerability in mozilla thunderbird. EPSS estimates a 0.21% chance of exploitation in the next 30 days, higher than 11% of scored vulnerabilities.
CVSS score
6.3/10
010
Medium · v3.1 (CVE.org)EPSS score
0.21%
0%100%
Low · Change unavailableKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Advisory lineage
Upstream 0 · Downstream 3 · Related 2Timeline
- 30-09-2026PublishedVulnerability first disclosed.
- 16-10-2026Last modifiedVulnerability information updated.
Description
An attacker could cause a heap buffer overflow by getting a user to open an email that is greater than or equal to 2GB in size. This vulnerability was fixed in Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4.
CVSS metrics
4 scores · 4 sources · 1 versionMedium 6.3Preferred score · CVE.org (CNA)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:LSources4 sources · 6.1–6.3
- NVDNIST6.1MediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:HDiffers
- OSV · DebianEcosystem advisory · calculated6.1MediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:HDiffers
- OSV · UbuntuEcosystem advisory · calculated6.1MediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:HDiffers
EPSS trend
Probability
0.21%
Chance of exploitation in the next 30 days
Percentile
11%
Versus all other CVEs
30-day change
Change unavailable
Change unavailable
01-10-202619-10-2026
EPSS score0.21%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.
- CWE-122Heap-based Buffer OverflowA heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
Affected systems
Debian1 product
- thunderbird< 1:140.17.0esr-1~deb12u1 | < 1:140.17.0esr-1~deb13u1 | < 1:153.4.0esr-1
Mozilla1 product
- thunderbird< 140.17.0 | ≥ 141.0, < 153.4.0 | ≥ 154.0, < 157.0
Ubuntu1 product
- thunderbirdAll versions (No fix recorded)
3 vendors · 3 products
