CVE-2026-120756: Heap Buffer Over-read via Malformed Message Size in HDF5's H5O__chunk_deserialize
CVE-2026-120756 is a vulnerability in Heap Buffer Over-read via Malformed Message Size in HDF5's H5O__chunk_deserialize, rated Low by Microsoft, with a CVSS 3.1 base score of 6.1 (Medium). An attacker can exploit it by an attacker with local access, without any privileges and only if a user takes an action. Microsoft has not reported exploitation in the wild. The EPSS model estimates a 0.18% probability of exploitation activity in the next 30 days, higher than 7% of all scored vulnerabilities. Microsoft released the fix on 5 November 2026, outside Patch Tuesday. It affects 1 product in 1 product family (Open Source Software).
Key facts
- CVE ID
- CVE-2026-120756
- Severity
- Medium CVSS 6.1
- Microsoft severity
- Low
- Exploited in the wild
- No
- Publicly disclosed
- No
- EPSS
- 0.18% (percentile 7%)
- CISA KEV
- Not listed
- Released
- Last updated
- Patch Tuesday
- November 2026 Patch Tuesday
- Product families
- Open Source Software
CVSS score and vector
Microsoft scores CVE-2026-120756 at 6.1 (temporal 6.1) using CVSS 3.1. Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H
| Metric | Value |
|---|---|
| Attack vector | Local |
| Attack complexity | Low |
| Privileges required | None |
| User interaction | Required |
| Scope | Unchanged |
| Confidentiality impact | Low |
| Integrity impact | None |
| Availability impact | High |
Affected products (1)
Open Source Software
| Product | Security update | Type | Fixed build | Restart |
|---|---|---|---|---|
| azl3 hdf5 1.14.6-6 on Azure Linux 3.0 | Release Notes | Security Update |
Revision history
| Version | Date | Description |
|---|---|---|
| 1.0 | Information published. |