CVE-2026-86251

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    CVE-2026-86251

    Published: 6 Sept 2026Last Modified: 11 Sept 2026

    Summary: h3 before 1.15.9 Path Traversal via Double Decoding

    Details: 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.

    References: https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86251.json, https://github.com/h3js/h3/security/advisories/GHSA-72gr-qfp7-vwhw, https://nvd.nist.gov/vuln/detail/CVE-2026-86251, https://www.vulncheck.com/advisories/h3-before-1.15.9-path-traversal-via-double-decoding

    Affected packages

    Package

    Name:

    Purl:

    Affected ranges

    Type: GIT

    Events:

    Introduced- 0
    Fixed -4e8d43a7703d0d5c8bbc09748db1d8b9f3c51b42

    Affected versions

    v1.15.7
    v1.15.6
    v1.15.5
    v1.15.4
    v1.15.2
    v1.15.1
    v1.15.0

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High
    CVE-2026-86251 | CVE-DB