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.
CVE-2026-103500
UNRATEDCVSS · not yet scoredTrending — 5 sources updated this week
—
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- No CVSS published and no exploitation signals yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS v2: —Exploit: None knownExposed services: Not assessed
No fix is confirmed yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for the fix.
- CVSS v3
- —
- EchelonGraph score
- Not yet assessedNo source has published severity data for this CVE yet — no CVSS score from NVD or a CNA, no GitHub advisory, and it is not in CISA KEV. This is not a rating of zero; we cannot assess it yet.
- EG Score
- —
- EG Risk
- —
- EPSS PROB
- 0.2%
- EPSS %ILE
- 9th
- KEV
- Not listed
Published
September 30, 2026
Last Modified
September 30, 2026
References (4)
- security@mozillahttps://bugzilla.mozilla.org/show_bug.cgi?id=2070267
- security@mozillahttps://www.mozilla.org/security/advisories/mfsa2026-101/
- security@mozillahttps://www.mozilla.org/security/advisories/mfsa2026-102/
- security@mozillahttps://www.mozilla.org/security/advisories/mfsa2026-103/
Vendor Advisories for CVE-2026-103500(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Affected Packages
(3 across 3 ecosystems)
Debian:12(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| thunderbird | 1:102.11.0-1 ... 1:140.9.1esr-1~deb13u1 (231 versions) |
| — |
Debian:13(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| thunderbird | 1:128.13.0esr-1 ... 1:140.9.1esr-1~deb13u1 (87 versions) |
| — |
Debian:14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| thunderbird | 1:128.13.0esr-1 ... 1:155.0.1-2 (102 versions) |
| — |
Data Freshness Timeline
(refreshed 9× in last 7d / 9× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-10-04 23:21 UTCEPSS rescore
- 2026-10-03 14:48 UTCEG score recompute
- 2026-10-03 14:48 UTCGHSA enrichment
- 2026-10-03 14:25 UTCEPSS rescore
- 2026-10-01 19:49 UTCEPSS rescore
- 2026-09-30 19:12 UTCGHSA enrichment
- 2026-09-30 18:24 UTCNVD update
- 2026-09-30 17:21 UTCEG score recompute
- 2026-09-30 17:20 UTCMITRE cvelistV5first tracked
Frequently asked(4)
What is CVE-2026-103500?
CVE-2026-103500 is a publicly disclosed vulnerability published on September 30, 2026. 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.
When was CVE-2026-103500 disclosed?
CVE-2026-103500 was first published on September 30, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-103500 actively exploited?
CVE-2026-103500 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (9th percentile of EPSS-scored CVEs).
How do I remediate CVE-2026-103500?
No fix for CVE-2026-103500 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix. The vendor advisories EchelonGraph has for CVE-2026-103500 are linked in the Vendor Advisories panel on this page.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-103500
Is Your Infrastructure Affected by CVE-2026-103500?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.