What is the CVSS score of CVE-2026-23527?

CVE-2026-23527 has a CVSS 3.1 base score of 8.9 (High). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L. EPSS exploitation probability: 0.0%.

Is there a public PoC exploit available for CVE-2026-23527?

Yes, a public proof-of-concept exploit is available for CVE-2026-23527. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2026-23527?

Within 7 days: Identify all affected systems and apply vendor patches promptly. Vendor patch is available.

H3 CVE-2026-23527

HIGH

HTTP Request/Response Smuggling (CWE-444)

2026-01-15 security-advisories@github.com

GHSA-mp2g-9vg9-f4cg

Information Disclosure Request Smuggling H3

8.9

CVSS 3.1 · GitHub Advisory

View

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

Access

Send HTTP request with case-variant Transfer-Encoding header
Exploit

Bypass case-sensitive header check
Execution

Smuggle request through proxy
Impact

Execute arbitrary actions on backend

Vulnerability Assessment

Weakness	CWE CWE-444 OWASP Top 10:2025 A06:2025 - Insecure Design ASVS 5.0 V4 - API and Web Service HTTP request consistency
Exploitation Conditions	H3 framework versions prior to 1.15.5 with readRawBody processing HTTP requests containing Transfer-Encoding headers. Requires intermediate proxy or HTTP/1.1 request forwarding to backend server for request smuggling to succeed.
Impact	CVSS 8.9 (HIGH). Attack vector: Network. Complexity: High. Privileges required: None. User interaction: None. Public exploit/POC available.
Exploit ScenarioDerived	An attacker could exploit this vulnerability to compromise the affected system.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

HTTP request smuggling in H3 framework versions before 1.15.5 allows remote attackers to bypass security controls by exploiting improper case-sensitive validation of the Transfer-Encoding header. The vulnerability enables attackers to inject malicious requests that diverge between client and server parsing, potentially leading to cache poisoning, session hijacking, or other attacks. Public exploit code exists for this vulnerability.

Earlier versions of this analysis (1)

v1 Mar 12, 2026 - 21:54 CVSS 8.9

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. [CVSS 8.9 HIGH]

RemediationAI

A vendor patch is available — apply it immediately. Fixed in version 1.15.5.. Restrict network access to the affected service where possible.

Affected Packages

npm h3 fix: 1.15.5

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in npm

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Classified as CWE-444 (HTTP Request/Response Smuggling). Affects H3. 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.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

GitHub Advisory PRIMARY 8.9 HIGH

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

Red Hat 8.9 HIGH

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

Low

Lifecycle Timeline

PoC Detected

Jan 23, 2026 - 18:50 vuln.today

Public exploit code

Patch released

Jan 23, 2026 - 18:50 nvd

Patch available

CVE Published

Jan 15, 2026 - 20:16 nvd

HIGH 8.9

DescriptionGitHub Advisory

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.

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

6 npm packages depend on h3 (6 direct, 0 indirect)

Ecosystem-wide dependent count for version 1.15.5.

Executive ViewAI

Why It Matters

CVE-2026-23527 presents significant security risk rated CVSS 8.9. Successful exploitation could significantly impact the confidentiality, integrity, or availability of affected systems. Proof-of-concept code is publicly available, increasing the risk of exploitation. A patch is available and should be applied as part of regular vulnerability management.

Business Impact: Severe

Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Implement network-level access controls to limit exposure; (2) Enable enhanced monitoring and alerting; (3) Apply principle of least privilege.

Threat Intelligence Overview

EPSS Score

0.0%

Top 92% exploitable

Threat Intel

1 source

Exploit

POC

Public exploit code exists

Data Quality

5 sources

Confidence: Medium

NVD

CVE.org

EPSS GHSA Vendor

GitHub

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV No

Public POC Yes

EPSS 0.0%

Patch available Yes

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Out-of-Cycle

Exploitation· derived

Poc

System Exposure· derived

Open

Automatable· derived

Human Impact

Very High

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +44

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

HTTP Request Smuggling HIGH

HTTP request smuggling exploits inconsistencies in how front-end and back-end servers parse HTTP message boundaries.

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.