CVE-2026-109478: ASP.NET Core Denial of Service Vulnerability
CVE-2026-109478 is a denial of service vulnerability in ASP.NET Core, rated Important by Microsoft, with a CVSS 3.1 base score of 7.5 (High). An attacker can exploit it remotely over the network, without any privileges and without user interaction. Microsoft has not reported exploitation in the wild and rates exploitation as less likely. Microsoft released the fix on 10 November 2026 in the November 2026 Patch Tuesday, delivered through 1 security update (KB5135243). It affects 6 products in 1 product family (Developer Tools).
Key facts
- CVE ID
- CVE-2026-109478
- Severity
- High CVSS 7.5
- Microsoft severity
- Important
- Impact
- Denial of Service
- Exploited in the wild
- No
- Publicly disclosed
- No
- Exploitation likelihood
- Less Likely
- CISA KEV
- Not listed
- Released
- Last updated
- Patch Tuesday
- November 2026 Patch Tuesday
- Product families
- Developer Tools
CVSS score and vector
Microsoft scores CVE-2026-109478 at 7.5 (temporal 6.5) using CVSS 3.1. Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C
| Metric | Value |
|---|---|
| Attack vector | Network |
| Attack complexity | Low |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality impact | None |
| Integrity impact | None |
| Availability impact | High |
| Exploit code maturity | Unproven |
| Remediation level | Official fix |
| Report confidence | Confirmed |
Description
Inefficient algorithmic complexity in ASP.NET Core allows an unauthorized attacker to deny service over a network.
Affected products (6)
Developer Tools
| Product | Security update | Type | Fixed build | Restart |
|---|---|---|---|---|
| .NET 8.0 installed on Windows | KB5135243 | Security Update | 8.0.34 | |
| .NET 8.0 installed on Linux | KB5135243 | Security Update | 8.0.34 | |
| .NET 8.0 installed on Mac OS | KB5135243 | Security Update | 8.0.34 | |
| Microsoft Visual Studio 2022 version 17.14 | Release Notes | Security Update | 17.14.45 | Yes |
| Microsoft Visual Studio 2026 version 18.11 | Release Notes | Security Update | 18.11.4 | |
| Microsoft Visual Studio 2026 version 18.12 | Release Notes | Security Update | 18.12.0 |
Security updates (1)
- KB5135243 (Security Update)
Acknowledgments
- Matteo Panzeri
Revision history
| Version | Date | Description |
|---|---|---|
| 1.0 | Information published. |