CVE-2026-86251— h3 before 1.15.9 Path Traversal via Double Decoding
Quick assessment
Affected
h3js h3
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
h3 版本 1.15.9 之前存在一个路径遍历漏洞，位于 工具中。由于存在双重解码缺陷，包含双重编码的点序列（例如 %252e%252e）的请求路径会被解码为 %2e%2e。由于 函数仅检查字面量字符 “.”，因此 %2e%2e 能够绕过该函数的检查并保留下来。当由此生成的资源 ID 由基于 URL 的后端（如 CDN、S3、对象存储）解析时，%2e%2e 会按照 RFC 3986 规范被解释为 “..”，从而允许路径遍历，进而从后端读取任意文件。
Possible ATT&CK Techniques 1 AI
T1083 · File and Directory Discovery
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I. Basic Information for CVE-2026-86251
Vulnerability Information
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Vulnerability Title
h3 before 1.15.9 Path Traversal via Double Decoding
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对路径名的限制不恰当(路径遍历)
Source: CVE Program / CVE List V5
Affected Products
II. Public POCs for CVE-2026-86251
| # | POC Description | Source Link | Shenlong Link |
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Vendor Advisories for CVE-2026-86251 (2)
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🔗 h3 before 1.15.9 Path Traversal via Double Decoding | Advisories | VulnCheck third-party-advisory
Same Patch Batch · h3js · 2026-09-06 · 5 CVEs total
| CVE-2026-86250 | 7.5 HIGH | h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked Cookie |
| CVE-2026-86253 | 5.9 MEDIUM | h3 before 1.15.6 Path Traversal via Percent-Encoded Dot Segments |
| CVE-2026-86205 | 5.4 MEDIUM | h3 before 2.0.1-rc.18 Open Redirect via redirectBack() |
| CVE-2026-86252 | 5.3 MEDIUM | h3 before 1.15.9 SSE Event Injection via Carriage Return |
IV. Related Vulnerabilities
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CVE-2026-86253
h3 before 1.15.6 Path Traversal via Percent-Encoded Dot Segm -
CVE-2026-86252
h3 before 1.15.9 SSE Event Injection via Carriage Return -
CVE-2026-86250
h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunke -
CVE-2026-86205
h3 before 2.0.1-rc.18 Open Redirect via redirectBack() -
CVE-2026-33490
h3: Missing Path Segment Boundary Check in `mount()` Causes
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CVE-2026-86253
h3 before 1.15.6 Path Traversal via Percent-Encoded Dot Segm -
CVE-2026-86252
h3 before 1.15.9 SSE Event Injection via Carriage Return -
CVE-2026-86205
h3 before 2.0.1-rc.18 Open Redirect via redirectBack() -
CVE-2026-86250
h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunke -
CVE-2026-33732
srvx is vulnerable to middleware bypass via absolute URI in
Same weakness: CWE-22
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CVE-2026-86253
h3 before 1.15.6 Path Traversal via Percent-Encoded Dot Segm -
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SonicWall NSM 文件上传存在Zip Slip漏洞 -
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Emlog: Zip Slip Path Traversal in Plugin/Template ZIP Upload
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