Is CVE-2026-86250 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-86250?

CVE-2026-86250 has a CVSS v3 severity of HIGH (7.5).

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CVE-2026-86250

Description

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 O(n²) cleanup loop that hangs the server process.