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CVE-2026-23527

34
FAUCET Score

CVE-2026-23527 describes a critical HTTP Request Smuggling vulnerability in the H3 framework, affecting versions prior to 1.15.5. The flaw stems from a case-sensitive check for the "Transfer-Encoding" header, which should be case-insensitive per RFC standards. This vulnerability carries a CVSS score of 9.8 (CRITICAL), indicating it can be exploited remotely with low complexity, leading to high impacts on confidentiality, integrity, and availability. While there is no evidence of active exploitation or public exploit code (Metasploit, Nuclei, ExploitDB), the vulnerability has garnered significant community discussion, with 11 mentions across various platforms.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.15.5CPE matchmatch criteria
cpe:2.3:a:h3:h3:*:*:*:*:*:node.js:*:*

CVSS Data

CVSS version used by this source: 3.1

8.9HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
LOW
Exploitability Score
2.2
Impact Score
6.0
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.58%
Probability of exploitation in next 30 days
EPSS Percentile
44.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0058 is in the 24th percentile among its peer group of 36,862 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

github_advisorypatch availablevia nvd_reference
View patch
npmpatch availablevia ghsa
Product: h3Fixed in: 1.15.5

Vendor Advisories (2)

npmGHSA-mp2g-9vg9-f4cghigh

h3 v1 has Request Smuggling (TE.TE) issue

Jan 15, 2026
redhatCVE-2026-23527Important

h3: h3: HTTP Request Smuggling due to improper case-sensitive parsing of Transfer-Encoding header

Jan 15, 2026

References

github.com / h3js/h3/commit/618ccf4f37b8b6148bea7f36040471af45bfb097
Patch
github.com / h3js/h3/releases/tag/v1.15.5
github.com / h3js/h3/security/advisories/GHSA-mp2g-9vg9-f4cg
ExploitVendor Advisory
simonkoeck.com / writeups/h3-transfer-encoding-request-smuggling