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Vulnerability record · CVE-2026-86251 · published 6 September 2026

CVE-2026-86251: Path traversal vulnerability

h3 versions before 1.15.9 contain a path traversal vulnerability in the serveStatic utility. A double-decoding flaw allows a request path containing double-encoded dot sequences (e.g. %252e%252e) to be decoded to %2e%2e, which survives resolveDotSegments() because that function only checks for literal '.' characters. When the resulting asset ID is resolved by URL-based backends (CDN, S3, object storage), %2e%2e is interpreted as '..' per RFC 3986, enabling path traversal to read arbitrary files from the backend.

8.2 CVSS 4.0 High EPSS 0.43% · top 65.5% CWE-22 · Path traversal Awaiting Analysis
8.2CVSS 4.0 base score
0.43%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
3References
9 Sep 2026Last modified by NVD

Description

h3 versions before 1.15.9 contain a path traversal vulnerability in the serveStatic utility. A double-decoding flaw allows a request path containing double-encoded dot sequences (e.g. %252e%252e) to be decoded to %2e%2e, which survives resolveDotSegments() because that function only checks for literal '.' characters. When the resulting asset ID is resolved by URL-based backends (CDN, S3, object storage), %2e%2e is interpreted as '..' per RFC 3986, enabling path traversal to read arbitrary files from the backend.

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
https://github.com/h3js/h3/security/advisories/GHSA-72gr-qfp7-vwhw
https://www.vulncheck.com/advisories/h3-before-1.15.9-path-traversal-via-double-decoding
https://github.com/h3js/h3/security/advisories/GHSA-72gr-qfp7-vwhw

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Source: NIST National Vulnerability Database (record CVE-2026-86251), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.