CVE-2026-103500
MEDIUM 6.3An 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.
NO EXPLOITATION SIGNALS
No known exploitation, public exploit, or elevated probability at this time. Track for changes.
Exploitation likelihood
0.2%chance of exploitation in 30 days · 11th percentile
○ In CISA KEV
○ Public exploit / PoC
Impact if exploited
6.3CVSS 3.1 · MEDIUM
- ConfidentialityLow
- IntegrityLow
- AvailabilityLow
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ✓Privileges: No account or privileges required
- ⚠User interaction: A user must take an action (click / open a file)
- ✓Complexity: No special conditions — reliably repeatable
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept & exploit code
- github-search Search GitHub for public PoC repos
Test against your own equipment
curl -s https://vulnpedia.com/cve/CVE-2026-103500/poc.jsonMachine-readable PoC index for this CVE (for automation).Listed for defensive triage, patch verification, and authorized testing on systems you own. Machine-readable: /cve/CVE-2026-103500/poc.json
Weakness (CWE)
- CWE-122: Heap-based Buffer Overflow
- CWE-787: Out-of-bounds write
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L
Known Affected Software Configurations
| Vendor | Product | Version range |
|---|---|---|
| Mozilla | Thunderbird | < 140.17.0 |
| Mozilla | Thunderbird | ≥ 141.0 and < 153.4.0 |
| Mozilla | Thunderbird | ≥ 154.0 and < 157.0 |
All CVSS metrics
- MEDIUM 6.3 v3.1 · ADP Primary
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L - MEDIUM 6.1 v3.1 · NVD Primary
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:H - MEDIUM 6.3 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L