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CVE-2026-62901 is a denial-of-service vulnerability in .NET affecting WebSocket frame parsing in System.Net.WebSockets. The flaw is caused by unchecked input controlling a loop condition during frame data reads. After a standard HTTP/1.1 or HTTP/2 upgrade to WebSockets, an unauthenticated attacker can send a crafted WebSocket frame header that advertises a very large payload length and then stop transmitting or half-close the connection. In the vulnerable code path, the frame-reading loop continues calling Stream.ReadAsync but does not correctly handle a 0-byte return at end-of-stream. Because the remaining byte count is only reduced by the number of bytes read, a 0-byte read leaves the loop condition unchanged and causes the parser to spin indefinitely. Microsoft’s fix adds an explicit end-of-stream check and raises a WebSocketException with ConnectionClosedPrematurely when the read returns 0.
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No public exploit code observed for this vulnerability.
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
9 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A denial-of-service vulnerability in WebSocket frame parsing where a crafted frame advertises a large payload length and then closes the connection, causing the parser to loop on EOF and consume CPU indefinitely.
.NET Denial of Service vulnerability.
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.