Bug 2529162 (CVE-2026-86250)

Summary: CVE-2026-86250 h3: h3: Denial of Service via unbounded chunked cookie processing
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in h3. This vulnerability allows a remote attacker to send a specially crafted cookie header with an excessively large chunk count. This action triggers an inefficient cleanup process within the `setChunkedCookie()` and `deleteChunkedCookie()` functions, consuming significant server resources. Consequently, the server process can hang, leading to a denial of service (DoS) for legitimate users.
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Description OSIDB Bzimport 2026-09-06 12:11:51 UTC
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.