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Flowise: SSRF Protection Bypass (TOCTOU & Default Insecure)

High severity GitHub Reviewed Published Apr 15, 2026 in FlowiseAI/Flowise • Updated Apr 18, 2026

Package

npm flowise (npm)

Affected versions

<= 3.0.13

Patched versions

3.1.0
npm flowise-components (npm)
<= 3.0.13
3.1.0

Description

Summary

The core security wrappers (secureAxiosRequest and secureFetch) intended to prevent Server-Side Request Forgery (SSRF) contain multiple logic flaws. These flaws allow attackers to bypass the allow/deny lists via DNS Rebinding (Time-of-Check Time-of-Use) or by exploiting the default configuration which fails to enforce any deny list.

Details

The flaws exist in packages/components/src/httpSecurity.ts.

Default Insecure: If process.env.HTTP_DENY_LIST is undefined, checkDenyList returns immediately, allowing all requests (including localhost).

DNS Rebinding (TOCTOU): The function performs a DNS lookup (dns.lookup) to validate the IP, and then the HTTP client performs a new lookup to connect. An attacker can serve a valid IP first, then switch to an internal IP (e.g., 127.0.0.1) for the second lookup.

PoC

Ensure HTTP_DENY_LIST is unset (default behavior).

Use any node utilizing secureFetch to access http://127.0.0.1.

Result: Request succeeds.

Scenario 2: DNS Rebinding

Attacker controls domain attacker.com and a custom DNS server.

Configure DNS to return 1.1.1.1 (Safe IP) with TTL=0 for the first query.

Configure DNS to return 127.0.0.1 (Blocked IP) for subsequent queries.

Flowise validates attacker.com -> 1.1.1.1 (Allowed).

Flowise fetches attacker.com -> 127.0.0.1 (Bypass).

Run the following for manual verification

// PoC for httpSecurity.ts Bypasses
import * as dns from 'dns/promises';

// Mocking the checkDenyList logic from Flowise
async function checkDenyList(url: string) {
    const deniedIPs = ['127.0.0.1', '0.0.0.0']; // Simplified deny list logic

    if (!process.env.HTTP_DENY_LIST) {
        console.log(\"⚠️  HTTP_DENY_LIST not set. Returning allowed.\");
        return; // Vulnerability 1: Default Insecure
    }

    const { hostname } = new URL(url);
    const { address } = await dns.lookup(hostname);

    if (deniedIPs.includes(address)) {
        throw new Error(`IP ${address} is denied`);
    }
    console.log(`✅ IP ${address} allowed check.`);
}

async function runPoC() {
    console.log(\"--- Test 1: Default Configuration (Unset HTTP_DENY_LIST) ---\");
    // Ensure env var is unset
    delete process.env.HTTP_DENY_LIST;
    try {
        await checkDenyList('http://127.0.0.1');
        console.log(\"[PASS] Default config allowed localhost access.\");
    } catch (e) {
        console.log(\"[FAIL] Blocked:\", e.message);
    }

    console.log(\"\
--- Test 2: 'private' Keyword Bypass (Logic Flaw) ---\");
    process.env.HTTP_DENY_LIST = 'private'; // User expects this to block localhost
    try {
        await checkDenyList('http://127.0.0.1');
        // In real Flowise code, 'private' is not expanded to IPs, so it only blocks the string \"private\"
        console.log(\"[PASS] 'private' keyword failed to block localhost (Mock simulation).\");
    } catch (e) {
        console.log(\"[FAIL] Blocked:\", e.message);
    }
}

runPoC();

Impact

Confidentiality: High (Access to internal services if protection is bypassed).

Integrity: Low/Medium (If internal services allow state changes via GET).

Availability: Low.

References

@igor-magun-wd igor-magun-wd published to FlowiseAI/Flowise Apr 15, 2026
Published to the GitHub Advisory Database Apr 16, 2026
Reviewed Apr 16, 2026
Last updated Apr 18, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L

EPSS score

Weaknesses

Time-of-check Time-of-use (TOCTOU) Race Condition

The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. Learn more on MITRE.

Server-Side Request Forgery (SSRF)

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-2x8m-83vc-6wv4

Source code

Credits

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