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CVE-2026-26127 is a denial-of-service vulnerability in .NET caused by an out-of-bounds read. The flaw is associated with decoding malformed Base64Url input and affects .NET 9.0, .NET 10.0, and Microsoft.Bcl.Memory; reporting also indicates impact to ASP.NET Core deployments using the affected components. A remote, unauthenticated attacker can send crafted malformed input over the network to a vulnerable .NET application, triggering the out-of-bounds read and causing the application to crash. The issue was publicly disclosed prior to patch availability, increasing defender urgency even though exploitation was assessed as unlikely.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
60 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An actively exploited out-of-bounds read vulnerability affecting Microsoft .NET 9.0/10.0 and Microsoft.Blazor.Memory.
A .NET denial-of-service vulnerability disclosed in Microsoft's Patch Tuesday release.
A denial-of-service vulnerability in Microsoft .NET that could allow an attacker to disrupt services through an out-of-bounds read.
A denial-of-service vulnerability in Microsoft .NET that could allow an attacker to disrupt services through an out-of-bounds read.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.