CVE-2021-20698

Q: What is the severity of CVE-2021-20698?

CVE-2021-20698 has a CVSS score of 9.8 (CRITICAL). This vulnerability in Sharp NEC Displays allows attackers to gain root privileges and execute arbitrary code remotely by sending specially crafted HTTP requests with specific characters. It affects numerous display models with firmware versions prior to specified thresholds. Organizations using these displays in networked environments are at risk.

9.8 CRITICAL

Remote Code Execution

📋 TL;DR

This vulnerability in Sharp NEC Displays allows attackers to gain root privileges and execute arbitrary code remotely by sending specially crafted HTTP requests with specific characters. It affects numerous display models with firmware versions prior to specified thresholds. Organizations using these displays in networked environments are at risk.

💻 Affected Systems

Products:

Sharp NEC Displays models: UN462A, UN462VA, UN492S, UN492VS, UN552A, UN552S, UN552VS, UN552, UN552V, UX552S, UX552, V864Q, C861Q, P754Q, V754Q, C751Q, V984Q, C981Q, P654Q, V654Q, C651Q, V554Q, P404, P484, P554, V404, V484, V554, V404-T, V484-T, V554-T, C501, C551, C431

Versions: Prior to R1.300 for UN/UX series, prior to R2.000 for V/C/P series, prior to R3.200 for P/V series with -T suffix

Operating Systems: Embedded display firmware

Default Config Vulnerable: ⚠️ Yes

Notes: All affected models with default configurations are vulnerable if network services are enabled.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete compromise of display device leading to persistence, lateral movement to other network devices, data exfiltration, or use as pivot point for attacks.

🟠

Likely Case

Display device compromise allowing unauthorized access, configuration changes, or use in botnets/DDoS attacks.

🟢

If Mitigated

Limited impact if displays are isolated on separate VLANs with strict network controls and no internet access.

🌐 Internet-Facing: HIGH - CVSS 9.8 indicates critical severity; internet-facing displays can be directly exploited.

🏢 Internal Only: HIGH - Even internally, attackers with network access can exploit this vulnerability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires sending HTTP requests with specific characters; no authentication needed.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: UN/UX series: R1.300 or later; V/C/P series: R2.000 or later; P/V series with -T suffix: R3.200 or later

Vendor Advisory: https://www.sharp-nec-displays.com/global/support/info/A5-1_vulnerability.html

Restart Required: Yes

Instructions:

1. Download firmware update from Sharp NEC support site. 2. Transfer to display via USB or network. 3. Install update via display menu. 4. Reboot display.

🔧 Temporary Workarounds

Network Isolation

all

Place displays on isolated VLAN with no internet access and restricted internal access.

Disable Network Services

all

Turn off network connectivity for displays if not required for operation.

🧯 If You Can't Patch

Implement strict network segmentation with firewall rules blocking all unnecessary traffic to displays
Monitor network traffic to displays for unusual HTTP requests or connections

🔍 How to Verify

Check if Vulnerable:

Check display firmware version in Settings > Information menu; compare with patched versions listed in advisory.

Check Version:

No command - check via display menu interface

Verify Fix Applied:

Confirm firmware version shows patched version after update; test HTTP interface if possible.

📡 Detection & Monitoring

Log Indicators:

Unusual HTTP requests to display management interface
Multiple failed login attempts or unusual access patterns

Network Indicators:

HTTP traffic to display ports with unusual parameters or patterns
Unexpected outbound connections from displays

SIEM Query:

source_ip="display_ip" AND (http_request CONTAINS "specific_characters" OR http_status=200 AND user_agent="malicious")

📊 Metadata

CVE ID: CVE-2021-20698

CVSS v3 Score: 9.8 (CRITICAL)

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

Published: June 7, 2021

Last Updated: November 21, 2024

📋 TL;DR

💻 Affected Systems

📦 What is this software?

C431 Firmware by Sharp Nec Displays

C501 Firmware by Sharp Nec Displays

C551 Firmware by Sharp Nec Displays

C651q Firmware by Sharp Nec Displays

C751q Firmware by Sharp Nec Displays

C861q Firmware by Sharp Nec Displays

C981q Firmware by Sharp Nec Displays

P404 Firmware by Sharp Nec Displays

P484 Firmware by Sharp Nec Displays

P554 Firmware by Sharp Nec Displays

P654q Firmware by Sharp Nec Displays

P754q Firmware by Sharp Nec Displays

Un462a Firmware by Sharp Nec Displays

Un462va Firmware by Sharp Nec Displays

Un492s Firmware by Sharp Nec Displays

Un492vs Firmware by Sharp Nec Displays

Un552 Firmware by Sharp Nec Displays

Un552a Firmware by Sharp Nec Displays

Un552s Firmware by Sharp Nec Displays

Un552v Firmware by Sharp Nec Displays

Un552vs Firmware by Sharp Nec Displays

Ux552 Firmware by Sharp Nec Displays

Ux552s Firmware by Sharp Nec Displays

V404 Firmware by Sharp Nec Displays

V404 T Firmware by Sharp Nec Displays

V484 Firmware by Sharp Nec Displays

V484 T Firmware by Sharp Nec Displays

V554 Firmware by Sharp Nec Displays

V554 T Firmware by Sharp Nec Displays

V554q Firmware by Sharp Nec Displays

V654q Firmware by Sharp Nec Displays

V754q Firmware by Sharp Nec Displays

V864q Firmware by Sharp Nec Displays

V984q Firmware by Sharp Nec Displays