CVE-2022-38393

Executive Summary

CVE-2022-38393 is a denial of service (DoS) vulnerability in the configuration service of the Asus RT-AX82U router, specifically within the cfg_server module's cm_processConnDiagPktList opcode. The vulnerability affects firmware version 3.0.0.4.386_49674-ge182230 and allows an unauthenticated, network-adjacent attacker to crash the configuration service by sending a specially-crafted packet. With a CVSS score of 7.5 (High) and an EPSS score of 0.18847 (97th percentile), this vulnerability poses a significant availability risk to affected devices. No patch is currently available, and no public exploit code has been observed.

Technical Analysis

The vulnerability resides in the cfg_server process, which is the configuration management daemon running on the Asus RT-AX82U router. The affected opcode, cm_processConnDiagPktList, is responsible for processing connection diagnostic packet lists — a function used to handle network diagnostics data sent to the router's configuration service.

The specific flaw involves improper handling of a specially-crafted network packet. When the cfg_server process receives a packet that triggers the cm_processConnDiagPktList opcode with malformed or unexpected content, the service fails to properly validate the packet structure, leading to a denial of service condition. This results in the configuration service crashing or becoming unresponsive, which can disrupt the router's administrative interface, configuration capabilities, and potentially certain network management functions.

The attack surface is the router's configuration service, which listens for network connections. Because the CVSS vector indicates AV:N (Network) and PR:N (No Privileges Required), the attacker does not need authentication and can trigger the vulnerability remotely, provided they can reach the service. The cfg_server process likely runs with elevated privileges (root or system-level) due to the nature of router configuration services, meaning a crash of this process could have broader implications for router stability.

Technical detail beyond this is limited by the NVD description. The description explicitly names cfg_server, cm_processConnDiagPktList, and the device model/firmware, but does not provide the packet structure, opcode encoding, or the exact parsing failure that leads to the DoS. Insufficient technical detail is available for a deeper code-level analysis.

Exploitation Scenarios

No public PoC available; attack chain is inferred from vulnerability class.

1. Reconnaissance/Target Identification: An attacker scans for exposed Asus RT-AX82U routers. Given that this is a consumer router, the configuration service is typically bound to the LAN interface, but it may also be exposed to the WAN if UPnP or port forwarding is misconfigured, or if the router's remote management feature is enabled. Shodan queries (e.g., title:'RT-AX82U') can identify internet-facing devices. The attacker would then probe the configuration service to confirm the exact firmware version (3.0.0.4.386_49674-ge182230) by querying the web interface or administrative endpoints.

2. Triggering the Flaw: The attacker crafts a network packet designed to target the cm_processConnDiagPktList opcode of the cfg_server process. The packet is sent to the configuration service's listening port. Because the vulnerability is in the packet-list processing logic, the attacker does not need to authenticate — the service processes the packet before any authorization checks occur. The crafted packet likely contains malformed connection diagnostic data that causes an out-of-bounds read, an assertion failure, or an infinite loop in the parsing routine.

3. Payload/Execution Method: The payload is a single, specially-crafted network packet. The vulnerability class is "uncontrolled resource consumption" (CWE-400), which suggests the malformed packet causes the service to consume excessive CPU, memory, or file descriptors, or to hit a fatal error path that terminates the process. No code execution is implied by the description — this is a pure availability attack.

4. Post-Exploitation Impact: After the cfg_server process crashes, the router's configuration service becomes unavailable. Users may lose access to the web-based admin interface, and any services that depend on the configuration daemon (e.g., dynamic DNS updates, firewall rule refreshes, VLAN management) may stop functioning. Depending on how robust the firmware's process supervision is, the service may restart automatically (leaving only a transient DoS window) or remain down until manual reboot. In a worst-case scenario, a persistent crash-loop could render the router unusable until a physical power cycle.

Impact Assessment

Business Impact: The primary impact is availability. A successful exploitation results in a denial of service for the router's configuration service. For a home or small-office router like the RT-AX82U, this means the administrative interface becomes unresponsive, and configuration changes cannot be applied. If the cfg_server failure cascades to other services (e.g., DNS, DHCP, firewall), the entire network could lose connectivity or routing functionality.

CVSS Analysis: The vector is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, yielding a base score of 7.5 (High). Key observations:

• AV:N (Network): Attackable from any reachable network interface.
• AC:L (Low Attack Complexity): No special conditions or race windows required.
• PR:N (No Privileges): No authentication needed — the service processes the packet before auth checks.
• UI:N (No User Interaction): The victim does not need to click or interact.
• C:N/I:N (No Confidentiality/Integrity Impact): Data exfiltration or tampering is not implied by the description.
• A:H (High Availability Impact): The service failure is complete and likely crashes the process.

Blast Radius: Affected devices are limited to Asus RT-AX82U routers running firmware version 3.0.0.4.386_49674-ge182230. No other firmware versions or device models are explicitly listed as vulnerable in the NVD data, though it is plausible that other RT-AX82U builds share the affected code path. The blast radius is therefore confined to a specific hardware model and a narrow firmware build.

Threat Context: The EPSS score of 0.18847 (97th percentile of exploited CVEs) indicates a relatively high active-exploitation likelihood compared to other disclosed vulnerabilities. However, the CISA KEV list does not include this CVE, and no in-the-wild campaigns have been publicly reported. The lack of public PoC and exploit code raises the practical exploitation barrier, but the high EPSS percentile suggests that threat actors may be probing for this flaw.

Detection Guidance

Sigma Rule

title: Asus RT-AX82U cfg_server DoS Attempt
id: 1a2b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects network traffic targeting the Asus RT-AX82U configuration service with patterns consistent with CVE-2022-38393 exploitation attempts.
author: Valtersit Threat Intelligence
logsource:
  category: network_connection
  product: firewall
detection:
  selection:
    destination.port: 80
    destination.port: 443
    destination.port: 8080
    destination.ip: "192.168.1.1"  # Common RT-AX82U default IP
    network.protocol: tcp
  condition: selection
  timeframe: 5m
fields:
  - destination.ip
  - destination.port
  - source.ip
  - source.port
falsepositives:
  - Legitimate administrative access to the router
  - Automated firmware update checks
level: medium
tags:
  - attack.t1190
  - cve.2022-38393
  - cwe.400

YARA Rule

rule Asus_RT_AX82U_cfg_server_DoS
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects network payloads targeting the Asus RT-AX82U cfg_server cm_processConnDiagPktList opcode (CVE-2022-38393)"
        cve = "CVE-2022-38393"
        date = "2025-04-15"
        severity = "high"
    strings:
        // Known device model signature in HTTP requests to admin interface
        $model = "RT-AX82U" ascii nocase
        // Firmware version string that may appear in requests
        $fw = "3.0.0.4.386_49674" ascii nocase
        // Common pattern in configuration service requests
        $cfg = "cfg_server" ascii nocase
        // Diagnostic-related keywords
        $diag = "diag" ascii nocase
        // Packet list keyword
        $pktlist = "pktlist" ascii nocase
    condition:
        uint16(0) == 0x6162 and any of them
}

Note: The YARA rule uses heuristics based on publicly-known device identifiers since the exact packet structure is not disclosed. High false-positive rates are expected in legitimate network traffic.

Suricata IDS Rule

alert tcp any any -> $HOME_NET 80,443,8080 (msg:"CVE-2022-38393 Asus RT-AX82U cfg_server DoS Attempt"; flow:to_server,established; content:"cfg_server"; nocase; content:"diag"; nocase; content:"RT-AX82U"; nocase; content:"3.0.0.4.386"; nocase; reference:cve,2022-38393; classtype:attempted-dos; sid:20253839301; rev:1;)

Note: The rule is heuristic and looks for the device model/firmware strings in HTTP payloads. The actual malicious packet may not contain these strings in cleartext. Adjust ports to match the router's actual management interface.

Elastic Detection

// Detect network traffic to RT-AX82U management ports with suspicious content
any where process.name == "httpd" or process.name == "cfg_server"
// Alternative: network-level detection
network where destination.ip == "192.168.1.1" and destination.port in (80, 443, 8080) and network.protocol == "tcp"
// For endpoint telemetry on the router (if accessible):
process where event.action == "process_terminated" and process.name == "cfg_server"
  and process.exit_code != 0
  and process.command_line contains "*diag*"

Splunk SPL Query

index=network sourcetype=firewall
| where dest_ip IN ("192.168.1.1", "192.168.0.1", "10.0.0.1")
| where dest_port IN (80, 443, 8080)
| stats count by src_ip, dest_ip, dest_port, _time
| where count > 10
| eval severity = "high", cve = "CVE-2022-38393", description = "Possible exploitation attempt against Asus RT-AX82U"
| table _time, src_ip, dest_ip, dest_port, count, severity, cve, description

Wazuh OSSEC Rule

<group name="asus,router,dos,">
  <rule id="100282" level="10">
    <if_sid>100281</if_sid>
    <match>cfg_server.*crashed|cfg_server.*stopped|cfg_server.*restarting</match>
    <description>CVE-2022-38393 - Asus RT-AX82U configuration service crashed, possible DoS attack</description>
    <group>asus_rt_ax82u_dos,</group>
  </rule>
  <rule id="100281" level="7">
    <decoded_as>syslog</decoded_as>
    <match>cfg_server</match>
    <description>Asus RT-AX82U cfg_server event observed</description>
    <group>asus_rt_ax82u_events,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No vendor patch, firmware update, or security advisory has been published for this vulnerability. The affected build (3.0.0.4.386_49674-ge182230) remains vulnerable as of the last tracked source review.

Immediate Mitigations:

1. Restrict access to the configuration service: Ensure the router's management interface is not exposed to the WAN. Disable remote management (WAN-side access) in the router settings.
2. Segment the network: Place the router's management interface on a trusted VLAN or restrict LAN access to the admin interface using firewall rules, allowing only specific management hosts.
3. Monitor for anomalous traffic: Deploy the detection rules above to identify probing or exploitation attempts. Watch for repeated connections to ports 80/443/8080 from unusual sources.
4. Disable UPnP: UPnP can inadvertently expose the configuration service externally. Disable it if not needed.

Patch/Upgrade Steps:

• Check Asus's support page for the RT-AX82U periodically for new firmware releases.
• Subscribe to Asus security advisories to receive notifications about patches for this CVE.
• If a newer firmware version becomes available, apply it immediately. Asus frequently addresses security issues in routine firmware updates, but no specific fix has been confirmed for this CVE.

Long-Term Hardening:

1. Disable remote management permanently. Access the router's admin interface only from trusted LAN hosts.
2. Use strong admin credentials and change the default username/password. While this vulnerability does not require authentication, defense-in-depth is prudent.
3. Enable automatic firmware updates if the RT-AX82U supports it, and manually verify monthly that the router is running the latest build.
4. Consider replacing the device if Asus does not release a patch within a reasonable timeframe. End-of-life or unpatched routers are a persistent security risk.
5. Implement network-level filtering: Place a firewall or IDS between the router's management interface and untrusted network segments.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2022-38393
2. Asus Support (RT-AX82U Firmware): https://www.asus.com/networking-iot-servers/wifi-routers/asus-wifi-routers/rt-ax82u/helpdesk_download/
3. EPSS Data (FIRST.org): https://www.first.org/epss/
4. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
5. Mitre ATT&CK T1190: https://attack.mitre.org/techniques/T1190/

Threat Actor Activity: No known threat actor campaigns have been publicly attributed to this CVE. The CISA KEV list does not include this vulnerability, and no exploit-in-the-wild evidence has been reported in open-source threat intelligence feeds. However, the high EPSS percentile (97%) suggests active scanning or exploitation chatter may be occurring in certain networks, making this a vulnerability worth prioritizing for detection and mitigation despite the lack of public proof-of-concepts.