CVE-2026-86250

h3 versions before 2.0.1-rc.18 contain a denial-of-service vulnerability in the setChunkedCookie() and deleteChunkedCookie() functions. The library fails to validate the chunk count parsed from user-controlled cookie values, allowing a remote, unauthenticated attacker to send a crafted cookie hea...

CVE-2026-86250 h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked Cookie

h3 versions before 2.0.1-rc.18 fail to validate the chunk count parsed from user-controlled cookie values in setChunkedCookie and deleteChunkedCookie functions. Attackers can send a crafted cookie header with an extremely large chunk count to trigger an On² cleanup loop that hangs the server...

H3: Unbounded Chunked Cookie Count in Session Cleanup Loop may Lead to Denial of Service

Summary The setChunkedCookie and deleteChunkedCookie functions in h3 trust the chunk count parsed from a user-controlled cookie value chunkedN without any upper bound validation. An unauthenticated attacker can send a single request with a crafted cookie header e.g., Cookie: h3=chunked999999 to a...