CVE-2024-21872

Executive Summary

CVE-2024-21872 describes an authentication bypass vulnerability in an unidentified embedded transmitter device (vendor, product, and version range unconfirmed). An unauthenticated remote attacker can manipulate a cookie value to bypass authentication, granting access to hidden pages that expose critical control operations for the transmitter. The NVD assigns a CVSS score of 7.5 (High), reflecting full confidentiality impact (C:H) without any requirement for credentials or user interaction (PR:N, UI:N). No public exploit code, Nuclei template, or CISA KEV inclusion exists at the time of writing, though the vulnerability class — cookie-based auth bypass — is trivially exploitable once the device is identified. The identity of the affected vendor remains unconfirmed, making targeted remediation dependent on asset discovery and vendor contact.

Technical Analysis

Vulnerability Class: Authentication Bypass via Cookie Manipulation (CWE-287: Improper Authentication).

The root cause lies in the device's web management interface, which fails to cryptographically bind session cookies to a server-side session or to validate cookie integrity on subsequent requests. The authentication mechanism likely relies on a client-side cookie (e.g., auth, session_id, role, admin) whose value is compared against a static server-side value or, worse, evaluated as a boolean flag on the server without any HMAC signature, timestamp check, or server-side session store.

Mechanism:

1. The device serves a login page (/login or /index.html) with a standard username/password form.
2. Upon (or without) login, the server sends a Set-Cookie header containing a session identifier or role indicator.
3. Because the cookie is not signed or randomized per-session, an attacker who can guess or modify the cookie value (e.g., changing role=user to role=admin or setting authenticated=true) will be granted elevated access on subsequent requests.
4. The "hidden pages" referenced in the NVD description are likely protected URLs (e.g., /admin/, /config, /maintenance, /status) that check only for the presence of the forged cookie rather than validating a server-side session token.

Attack Surface:

• Network-accessible management interface: The device is a "transmitter" — a broad category that could include broadcast transmitters, IoT gateways, ICS/SCADA radio relays, or telemetry units. These are frequently deployed on exposed IPs for remote management.
• HTTP/HTTPS service: Typically bound to port 80 (HTTP) or 443 (HTTPS).
• Cookie scope: The vulnerable cookie is sent over the management protocol; if HTTPS is used, the attacker must intercept network traffic or rely on the cookie being set over plaintext HTTP (common in legacy embedded devices).

Code-Level Explanation (Illustrative):

A typical vulnerable implementation might look like (pseudo-code):

# Vulnerable: cookie value is trusted without validation
def handle_request(request):
    auth_cookie = request.cookies.get('authenticated')
    if auth_cookie == 'yes':
        return serve_admin_panel()
    else:
        return serve_login_page()

Or:

// Vulnerable: client-side role flag
String role = request.getCookie("role").getValue();
if (role.equals("admin")) { /* show critical ops */ }

No server-side session store, no HMAC, no signature check. Any client can set authenticated=yes or role=admin.

Known Limitations: The vulnerability specifically targets hidden pages that allow "more critical operations" — meaning basic authenticated access may already be possible, but the bypass grants escalated functionality (e.g., firmware flash, power output control, frequency tuning, or diagnostic reset).

Exploitation Scenarios

Scenario: Remote Takeover of an Unauthenticated Transmitter Control Interface

Reconnaissance (Step 1):

• Use Shodan or Censys with targeted dorks (http.title:"transmitter", http.html:"login" "transmitter") to identify internet-facing devices.
• Alternatively, conduct a network scan of ICS/SCADA segments (e.g., nmap -p 80,443,8080 --open 192.168.1.0/24).
• Fingerprint the device: fetch /robots.txt, /, and common firmware paths; identify the exact transmitter model (vendor-specific login page logos or HTML comments).

Trigger / Weaponization (Step 2):

1. Send a simple HTTP GET request to the device's root or login page to observe the Set-Cookie header. Record the cookie name (e.g., auth, session, priv).

2. Intercept or brute-force the cookie value. Common values:

   • auth=1, auth=0, authenticated=true, authenticated=false
   • role=admin, role=user, admin=yes
   • session_id=00000000000000000000000000000000 (all zeros often bypasses)

3. Use a crafted request with the modified cookie header:

   GET /admin/config HTTP/1.1
   Host: <target_ip>
   Cookie: auth=1; role=admin
   

4. If the device returns HTTP 200 with a configuration page or administrative panel, the bypass is confirmed.

Payload / Execution (Step 3):

• Once in the hidden admin page ("critical operations"), an attacker can:
  • Modify transmission frequencies or power output — potentially disrupting broadcast services or causing physical damage to the transmitter hardware.
  • Upload malicious firmware via the update mechanism — achieving persistent remote code execution on the device.
  • Extract encryption keys or authentication credentials from the device configuration (e.g., SNMP community strings, uplink passwords).
  • Reset or brick the device (denial of service).

Post-Exploitation (Step 4):

• Establish a foothold: upload a web shell or a reverse shell payload if the device supports arbitrary file upload via the admin panel.
• Pivot into the operational network: the transmitter may be dual-homed on both the internet and an internal OT network; leverage the compromised device to scan internal segments.
• Persistence: modify the device's startup scripts (if writable) or leave the firmware in a permanently modified state.

Note: The exact exploitability depends on the real vendor; however, the cookie-manipulation class is universally usable against devices that do not sign/randomize their session tokens.

Impact Assessment

Business Impact:

• Confidentiality (C:H): Critical configuration data, credentials, and operational parameters are exposed to unauthenticated attackers.
• Integrity (I:L): An attacker can modify settings but may not be able to alter firmware without additional steps (though this is plausible if the admin panel exposes an update function).
• Availability (A:N): Direct availability impact is not scored (A:N), but malicious frequency/power changes could physically damage equipment, causing indirect availability loss.

Affected Systems:

• All devices of the unconfirmed vendor/model running web-management firmware with cookie-based auth. Given the NVD description mentions "more critical operations to the transmitter," the device is likely a professional broadcast, RF, or telemetry transmitter.
• The inability to name the vendor increases blast radius — any enterprise with industrial broadcast or IoT transmitter assets should perform a sweep for unknown devices exposing web panels.

Blast Radius:

• Network scope: The management interface is reachable via the network; if placed on the public internet (common for remote telemetry), the entire attack surface is opened.
• OT/ICS overlap: If the transmitter bridges control networks, compromise can facilitate lateral movement into industrial control systems, violating segmentation boundaries.

CVSS Subscore Reasoning:

• Attack Vector: Network — requires no adjacent access.
• Attack Complexity: Low — cookie guessing/manipulation is trivial.
• Privileges Required: None — the bypass works from an unauthenticated state.
• User Interaction: None — no victim interaction needed.
• Scope: Unchanged — compromise stays within the device's security authority.

Detection Guidance

Sigma Rule

title: CVE-2024-21872 - Auth Bypass via Cookie Manipulation on Transmitter Device
id: 5f04a0d3-9a12-4b45-9cd3-5e3b7a2d1c44
status: experimental
description: Detects attempts to access hidden administrative pages with forged cookies on embedded transmitter devices.
author: Valtersit Threat Intel
date: 2024/04/01
tags:
  - attack.initialaccess
  - attack.t1190
  - cve.2024-21872
logsource:
  category: webserver
  product: httpd
detection:
  selection:
    cs-method: 'GET'
    cs-uri-query|contains:
      - '/admin/'
      - '/config'
      - '/maintenance'
    cs-cookie|contains:
      - 'auth=1'
      - 'auth=true'
      - 'role=admin'
      - 'authenticated=true'
  condition: selection
level: high
falsepositives:
  - Legitimate admin users with actual sessions may have similar cookies; correlate with source IP and session age.
fields:
  - clientip
  - cs-uri-query
  - cs-cookie
  - host

YARA Rule

rule CVE_2024_21872_Transmitter_Auth_Bypass {
    meta:
        author = "Valtersit Threat Intel"
        date = "2024-04-01"
        description = "Detects web responses containing hidden admin links or cookie handling patterns typical of vulnerable transmitter firmware."
        cve = "CVE-2024-21872"
    strings:
        $cookie_name1 = "auth" ascii nocase
        $cookie_name2 = "role" ascii nocase
        $cookie_name3 = "session" ascii nocase
        $admin_path1 = "/admin" ascii nocase
        $admin_path2 = "/maintenance" ascii nocase
        $critical_op = "power" ascii nocase
        $firmware_upload = "upload" ascii nocase
        $transmitter = "transmitter" ascii nocase
    condition:
        (uint16(0) == 0x4D5A or uint32(0) == 0x464C457F) and // PE or ELF binary
        (2 of ($cookie_name*) and 1 of ($admin_path*)) or
        (filesize < 2MB and $transmitter and any of ($cookie_name*))
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"CVE-2024-21872 - Unauthenticated Admin Access - Cookie Forge"; flow:to_server,established; http.method; content:"GET"; http.uri; content:"/admin/"; http.cookie; content:"auth"; nocase; http.cookie; content:"1"; http.cookie; content:"role"; nocase; http.cookie; content:"admin"; nocase; classtype:attempted-admin; sid:20242187; rev:1; metadata:created_at 2024_04_01, updated_at 2024_04_01, cve CVE-2024-21872, severity high;)

Elastic Detection

sequence by host.name with maxspan=5m
  [ network where event.type == "start" and destination.port in (80, 443, 8080) ]
  [ http where
      http.request.method == "GET" and
      (http.request.uri.path == "/admin/*" or http.request.uri.path == "/config/*") and
      http.request.body.content contains "auth" and
      http.request.body.content contains "1" and
      http.request.body.content contains "role" and
      http.request.body.content contains "admin" and
      source.ip != "127.0.0.1"
  ]

Splunk SPL Query

index=web earliest=-24h latest=now
| search (uri="*/admin/*" OR uri="*/config/*" OR uri="*/maintenance/*")
| regex cookie="(auth=1|authenticated=true|role=admin)"
| stats count by src_ip, uri, host, cookie
| where count < 20
| eval suspicious = if(like(lower(cookie), "%auth=1%") OR like(lower(cookie), "%role=admin%"), "HIGH", "MEDIUM")
| table _time, src_ip, dest_ip, host, uri, cookie, suspicious
| sort -_time

Wazuh OSSEC Rule

<group name="web, attack, cve_2024_21872,">
  <rule id="100872" level="12">
    <decoded_as>json</decoded_as>
    <field name="http.method">GET</field>
    <field name="url" type="pcre2">(/admin/|/config|/maintenance)</field>
    <field name="http.cookie" type="pcre2">(auth(=|%3D)1|authenticated(=|%3D)true|role(=|%3D)admin)</field>
    <description>CVE-2024-21872: Attempted auth bypass via cookie manipulation on transmitter web interface</description>
    <group>authentication_failed,</group>
    <mitre>
        <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 2/4 — CLAIMED (single source claims patch; not independently confirmed). Do not rely solely on vendor patches until the vendor is identified and an advisory is published.

1. Immediate Mitigations (No Patch Available):

   • Isolate device segment: Place all transmitter management interfaces behind a strict firewall; only allow management from trusted jump hosts or VPN IPs.
   • Disable remote management: If the device supports local-only (serial/USB) management, disable the web interface or bind it to localhost.
   • Place reverse proxy: Deploy a reverse proxy (e.g., nginx, HAProxy) in front of the device that enforces mutual TLS and require the proxy to inject a valid, signed session cookie — invalidating any client-supplied cookie.
   • Network-layer blocking: Block inbound HTTP(S) from non-whitelisted IPs on the device's management port using ACLs on the perimeter firewall.
   • Monitor access: Enable verbose device logging (if supported) and feed logs to the SIEM using the rules above.

2. Patch / Upgrade Steps:

   • Identify vendor: Determine the exact transmitter model (check web page title, footer, HTML comments, or MAC OUI lookup). Contact the hardware vendor's security team with CVE-2024-21872 reference.
   • Apply vendor patch: Request a firmware update that replaces cookie-only authentication with server-side session tokens (e.g., using HMAC-signed cookies or a session store). Validate the patch against the device's release notes.
   • Test in staging: Deploy the patch on a non-production unit first; confirm the auth bypass no longer works by repeating the cookie forgeries described in this report.
   • Fallback: If no patch exists, request the vendor to provide a custom firmware build or a configuration option to disable cookie-based auth entirely.

3. Long-Term Hardening:

   • Decommission legacy devices: Replace transmitters that cannot be patched with modern units supporting proper session management and TPM-backed device identity.
   • Implement network segmentation: Place transmitter networks in a separate VLAN/VRF with stateful inspection between OT and IT zones.
   • Enable encrypted management: Force HTTPS with modern TLS (1.2+) and disable HTTP entirely if the firmware allows it.
   • Conduct annual firmware review: Track firmware versions and subscribe to vendor security advisories (or NVD feed) to catch future flaws early.
   • Adopt zero-trust for OT: Require certificate-based authentication for all devices that support it; use a PKI for device identity.

References

1. NVD Entry — CVE-2024-21872
   https://nvd.nist.gov/vuln/detail/CVE-2024-21872
   Provides the authoritative description and CVSS score (7.5) as of publication.

2. CWE-287: Improper Authentication
   https://cwe.mitre.org/data/definitions/287.html
   Vulnerability classification and description of the underlying weakness.

3. MITRE ATT&CK — T1190: Exploit Public-Facing Application
   https://attack.mitre.org/techniques/T1190/
   Relevant tactic/technique mapping for initial access via the exposed web interface.

4. U.S. Cybersecurity and Infrastructure Security Agency (CISA) — Known Exploited Vulnerabilities Catalog
   https://www.cisa.gov/known-exploited-vulnerabilities-catalog
   Checked for CVE-2024-21872 — NOT currently listed (no evidence of in-the-wild exploitation or KEV inclusion).

5. FIRST.org — EPSS (Exploit Prediction Scoring System)
   https://www.first.org/epss/
   CVE-2024-21872 has not yet been scored by FIRST.org as of this report; no EPSS probability can be attached.

Threat Actor Campaigns / Exploit-in-the-Wild Evidence:
No known threat actor campaigns have been publicly attributed to CVE-2024-21872. The NVD entry and all major CVE feeds indicate no public exploit code exists (no Metasploit module, no Exploit-DB entry, no GitHub proof-of-concept). The single "claimed" patch source is unverified, and no vendor has yet acknowledged the vulnerability. Given the cookie-bypass class, exploitation is likely trivial once a vulnerable device is identified, making proactive asset discovery and monitoring a priority.