Server hang via unbounded cookie cleanup loop
Published Sep 6, 2026 · Updated Sep 6, 2026
Denial of service in h3js h3 before 2.0.1-rc.18 allows remote attackers to hang server processes via crafted cookie headers. getChunkedCookieCount() accepts an unbounded count from the __chunked__N sentinel, and cleanup in setChunkedCookie() or deleteChunkedCookie() repeatedly scans headers for every claimed chunk. An unauthenticated request reaches the loop only on an endpoint using session helpers, where the single-threaded process stops handling other requests.
Summary
What happened
Denial of service in h3js h3 before 2.0.1-rc.18 allows remote attackers to hang server processes via crafted cookie headers. getChunkedCookieCount() accepts an unbounded count from the __chunked__N sentinel, and cleanup in setChunkedCookie() or deleteChunkedCookie() repeatedly scans headers for every claimed chunk. An unauthenticated request reaches the loop only on an endpoint using session helpers, where the single-threaded process stops handling other requests.
The record
- CVE
- CVE-2026-86250
- Published
- Sep 6, 2026
- Updated
- Sep 6, 2026
- Vendor
- Uber
- Product
- H3
- Classifications
- CWE-400, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 6, 2026CVE publishedPublication date reported by the CVE source.
- Sep 6, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=2.0.0-beta.4 <2.0.1-rc.18
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- GHSA-q5pr-72pq-83v3 proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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