CVE-2026-86250

High

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.

SeverityHigh

CVSS7.5

Exploit probability—

ProductH3

PublishedSep 6, 2026

First seenSep 6, 2026

Weakness typeCWE-400Uncontrolled resource consumption

How to fix

Update

h32.0.1-rc.18 or later

Vendor advisories

github.com/h3js/h3/security/advisories/GHSA-q5pr-72pq-83v3

Affected products

Product	Affected versions	Fixed in
h3npm	2.0.0-beta.4 ≤ v < 2.0.1-rc.18	2.0.1-rc.18

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