CVE-2026-86250 PUBLISHED

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

Assigner: VulnCheck
Reserved: 06.09.2026 Published: 06.09.2026 Updated: 06.09.2026

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 Vector: 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
CVSS Score: 8.7

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	Low	Integrity	None	Integrity	None
Attack Requirements	None	Availability	High	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 7.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	None
User Interaction	None	Availability Impact	High

CVSS 3.1

Product Status

Vendor	h3js
Product	h3
Versions	Default: unaffected affected from 2.0.0-beta.4 to 2.0.1-rc.18 (excl.) Version 2.0.1-rc.18 is unaffected

CVE-2026-86250 PUBLISHED

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

Metrics

Product Status

Credits

References

Problem Types