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TI-2026-18951 Aliases CVE-2026-23527GHSA-mp2g-9vg9-f4cg

h3 v1 has Request Smuggling (TE.TE) issue

Priority MEDIUM 44CWE-444Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
High · High · High
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and GitHub.

Summary

H3 is a minimal H(TTP) framework built for high performance and portability. Prior to 1.15.5, there is a critical HTTP Request Smuggling vulnerability. readRawBody is doing a strict case-sensitive check for the Transfer-Encoding header. It explicitly looks for "chunked", but per the RFC, this header should be case-insensitive. This vulnerability is fixed in 1.15.5.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00626 50th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed h3 (h3js): 1.15.5h3 (npm): 1.15.5

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Total

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 1.15.51.15.5Patch availableCNA
—h3 (npm)before 1.15.51.15.5Patch availableGHSA-mp2g-9vg9-f4cg
  • h3 Vendorh3js Affected before 1.15.5 Fixed in 1.15.5 Patch available CNA
  • h3 (npm) Vendor— Affected before 1.15.5 Fixed in 1.15.5 Patch available GHSA-mp2g-9vg9-f4cg

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:h3:h3:*:*:*:*:*:node.js:*:*before 1.15.5Vulnerableh3js
  • cpe:2.3:a:h3:h3:*:*:*:*:*:node.js:*:* Versions before 1.15.5 Vulnerable ·h3js

Remediation

  • Fix · CNA h3 (h3js) Fixed in 1.15.5
  • Fix · GHSA-mp2g-9vg9-f4cg h3 (npm) Fixed in 1.15.5 Advisory →

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product
  • Red Hat

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-23527
  2. 2026-10-03 Alias added: GHSA-mp2g-9vg9-f4cg
  3. 2026-10-31 EPSS moved to the 50th–90th percentile

References

Exploit 1

Patch 1

Advisory 1

Other 3

  • 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-2026-25560 h3 has an observable timing discrepancy in basic auth utils CVSS 3.1MEDIUM 5.9
  • TI-2026-25886 h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes CVSS 3.1MEDIUM 5.3

Sources

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