What is CVE-2026-33115?
A remote code execution vulnerability exists in .NET and Visual Studio due to unsafe deserialization in the BinaryFormatter fallback path. An attacker who successfully exploits this vulnerability could execute arbitrary code on the target system. The vulnerability was disclosed as part of the Microsoft April 2026 Patch Tuesday release, which remediated 167 vulnerabilities across Windows, Office, SharePoint, .NET, Defender, Active Directory, Remote Desktop, Azure, Hyper-V, and supporting components. This CVE was rated Critical severity with a CVSS 8.1 base score. Exploitation requires an attacker to craft a malicious serialized object that triggers the BinaryFormatter deserialization path, which can lead to full code execution in the context of the application.
The record classifies CVE-2026-33115 under weakness class CWE-502. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. 2 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 197 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 8.1 — HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H - EPSS (FIRST)
- 0.3% probability of exploitation in the next 30 days, higher than 28.2% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 5.2/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-04-14, last modified 2026-09-25
Is CVE-2026-33115 being exploited?
It currently carries a trending score of 12 in the Threadlinqs vulnerability feed.
Affected products and versions
- Microsoft: .NET, Visual Studio
How to fix CVE-2026-33115
The record marks a vendor fix as available for CVE-2026-33115. Patch reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33115. Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33115. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-33115
2 tracked threats in the Threadlinqs corpus reference CVE-2026-33115, either in the campaign’s CVE list or as an indicator on the campaign record.
- Microsoft April 2026 Patch Tuesday — 163 CVEs / 88 Advisories (CVE-2026-32201 SharePoint Zero-Day Exploited In-The-Wild, CVE-2026-33825 Defender EoP Public PoC, CVE-2026-33824 IKE RCE CVSS 9.8, CVE-2026-33827 TCP/IP Wormable RCE) — CRITICAL · 2026-04-19
- Microsoft April 2026 Patch Tuesday — 167 Flaws, 2 Zero-Days (SharePoint Spoofing CVE-2026-32201 + Defender EoP CVE-2026-33825) — CRITICAL · 2026-04-14
Sources
Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on .