Read the docs
TI-2026-59037 Aliases CVE-2026-86251GHSA-676v-2c25-vqpj

h3 before 1.15.9 Path Traversal via Double Decoding

Priority HIGH 69CWE-22Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Attack requirements
Present
Impact type
Information disclosure
Confidentiality · integrity · availability
High · None · None
Fix status
Partial Red Hat: 1 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-22 and the CVSS impact.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00428 37th percentileScored 2026-11-07
Fix Partial h3 (h3js): 1.15.9Red Hat: 1 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
h3jsh3before 1.15.91.15.9Patch availableCNA
  • h3 Vendorh3js Affected before 1.15.9 Fixed in 1.15.9 Patch available CNA

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:h3:h3:*:*:*:*:*:*:*:*——h3js
  • cpe:2.3:a:h3:h3:*:*:*:*:*:*:*:* Versions — — ·h3js

Remediation

  • Fix · CNA h3 (h3js) Fixed in 1.15.9

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat OpenShift AI (RHOAI)AffectedNo fix yet: Fix deferred

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-86251
  2. 2026-10-03 Alias added: GHSA-676v-2c25-vqpj

References

Advisory 1

  • TI-2026-25559 h3 has a Server-Sent Events Injection via Unsanitized Newlines in Event Stream Fields CVSS 3.1CRITICAL 10.0
  • TI-2026-25562 h3 has a middleware bypass with one gadget CVSS 3.1CRITICAL 9.1
  • TI-2026-59038 h3 before 1.15.9 SSE Event Injection via Carriage Return CVSS 4.0MEDIUM 6.9
  • TI-2026-25560 h3 has an observable timing discrepancy in basic auth utils CVSS 3.1MEDIUM 5.9
  • TI-2026-58994 h3 before 2.0.1-rc.18 Open Redirect via redirectBack() CVSS 4.0MEDIUM 5.3
  • TI-2026-25886 h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes CVSS 3.1MEDIUM 5.3
See all 10 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences