CVE-2026-86250: high-severity vulnerability in h3js h3
h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked Cookie
Published · Updated
E-mail alert when it lands in KEV, gets a public PoC or its score goes up.
21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 8.7epss 0.5%
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.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Affected products
h3js · h3Related CVEs — h3js h3
In the same product, most dangerous first.
CVE-2026-23527HIGHh3 v1 has Request Smuggling (TE.TE) issueEPSS 0.6%CVE-2026-86253HIGHh3 before 1.15.6 Path Traversal via Percent-Encoded Dot SegmentsEPSS 0.6%CVE-2026-33128HIGHh3 has a Server-Sent Events Injection via Unsanitized Newlines in Event Stream FieldsEPSS 0.6%CVE-2026-86251HIGHh3 before 1.15.9 Path Traversal via Double DecodingEPSS 0.4%CVE-2026-33131HIGHh3 has a middleware bypass with one gadgetEPSS 0.4%CVE-2026-86252MEDIUMh3 before 1.15.9 SSE Event Injection via Carriage ReturnEPSS 0.4%