ASP.NET Core: Denial of service via inefficient algorithm in validation
Summary
A flaw in ASP.NET Core allows an unauthenticated remote attacker to cause a denial of service. Attacker-controlled collections can trigger heavy CPU work after the client has disconnected, which affects availability only. The CVE record lists affected .NET 11 builds on Linux, macOS and Windows, the Microsoft.Extensions.Validation package and Visual Studio 2026 version 18.12.
Affected
- Microsoft .NET 11.0 (11.0.0-preview.1 to before 11.0.0) on Linux, macOS and Windows
- Microsoft.Extensions.Validation (11.0.0-rc.1.26425.128 to before 11.0.0)
- Visual Studio 2026 version 18.12: range unclear in the CVE record, check the MSRC advisory
Fixed in
- .NET 11.0.0 and Microsoft.Extensions.Validation 11.0.0 (implied by the CVE record; confirm exact patched versions on the MSRC advisory)
- Visual Studio 2026 18.12: fixed version unknown, check the MSRC advisory
Workaround
Unknown.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact partial
- Not listed in CISA KEV; OffSeq: not known to be exploited
- No public proof of concept found; Rapid7: exploitation less likely
Our recommendation
- Identify .NET 11 applications, the Microsoft.Extensions.Validation package and Visual Studio 18.12 installations
- Check whether these applications use Minimal APIs with validation and are reachable from the internet
- Apply the fixed packages from the MSRC advisory, then restart and redeploy; prioritise internet-exposed APIs
- Monitor request latency and CPU usage on affected services
- Systems on .NET 8, 9 or 10 are not in the listed scope
Information from Microsoft (Patch Tuesday November 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide: CVE-2026-118749 msrc.microsoft.com
- CVE.org record CVE-2026-118749 www.cve.org
- .NET announcements issue 505 (advisory mirror) github.com
- .NET and .NET Framework November 2026 servicing updates devblogs.microsoft.com
- Rapid7 Patch Tuesday November 2026 www.rapid7.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 05:34.
Original description (NVD)
Inefficient algorithmic complexity in ASP.NET Core allows an unauthorized attacker to deny service over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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