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Rt Ax55 Firmware CVE-2023-39240

HIGH
Use of Externally-Controlled Format String (CWE-134)
2023-09-07 twcert@cert.org.tw
7.2
CVSS 3.1 · Vendor: cert
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Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V1 - Encoding and Sanitization Format string safety
Impact

CVSS score of 7.2 (HIGH). Attack characteristics: network attack vector, low complexity, high privileges required, no user interaction not required.

Exploit ScenarioDerived

This vulnerability can be exploited remotely over the network. Successful exploitation could compromise the high-severity affected system.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
No patch listed yet 1.2% exploitation probability (EPSS)

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AnalysisAI

It is identified a format string vulnerability in ASUS RT-AX56U V2’s iperf client function API. Rated high severity (CVSS 7.2), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affects your stack

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Technical ContextAI · show details

This vulnerability is classified under CWE-134. It is identified a format string vulnerability in ASUS RT-AX56U V2’s iperf client function API. This vulnerability is caused by lacking validation for a specific value within its set_iperf3_cli.cgi module. A remote attacker with administrator privilege can exploit this vulnerability to perform remote arbitrary code execution, arbitrary system operation or disrupt service. Affected products include: Asus Rt-Ax55 Firmware, Asus Rt-Ax56U V2 Firmware, Asus Rt-Ac86U Firmware.

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Severity by source

Vendor (cert) PRIMARY 7.2 HIGH
AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Primary rating from Vendor (cert) · only source for this CVE.

CVSS VectorVendor: cert

Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionCVE.org

It is identified a format string vulnerability in ASUS RT-AX56U V2’s iperf client function API. This vulnerability is caused by lacking validation for a specific value within its set_iperf3_cli.cgi module. A remote attacker with administrator privilege can exploit this vulnerability to perform remote arbitrary code execution, arbitrary system operation or disrupt service.

Threat Intelligence Overview

EPSS Score
1.2%
Top 37% exploitable
Data Quality
2 sources
Confidence: Low

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 1.2%
Patch available No
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

37
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +36
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

Affected Products (CPE)CVE.org

cpe:2.3:o:asus:rt-ax55_firmware:3.0.0.4.386_50460:*:*:*:*:*:*:*
cpe:2.3:o:asus:rt-ax56u_v2_firmware:3.0.0.4.386_50460:*:*:*:*:*:*:*
cpe:2.3:o:asus:rt-ac86u_firmware:3.0.0.4_386_51529:*:*:*:*:*:*:*
CVE-2022-26376 CRITICAL POC
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A memory corruption vulnerability exists in the httpd unescape functionality of Asuswrt prior to 3.0.0.4.386_48706 and A

CVE-2023-39780 HIGH POC
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On ASUS RT-AX55 3.0.0.4.386.51598 devices, authenticated attackers can perform OS command injection via the /start_apply

CVE-2021-41435 CRITICAL
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CVE-2023-41347 HIGH
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ASUS RT-AX55’s authentication-related function has a vulnerability of insufficient filtering of special characters withi

CVE-2023-41346 HIGH
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ASUS RT-AX55’s authentication-related function has a vulnerability of insufficient filtering of special characters withi

CVE-2023-41345 HIGH
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ASUS RT-AX55’s authentication-related function has a vulnerability of insufficient filtering of special characters withi

CVE-2021-41436 HIGH
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An HTTP request smuggling in web application in ASUS ROG Rapture GT-AX11000, RT-AX3000, RT-AX55, RT-AX56U, RT-AX56U_V2,

CVE-2021-3128 HIGH
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In ASUS RT-AX3000, ZenWiFi AX (XT8), RT-AX88U, and other ASUS routers with firmware < 3.0.0.4.386.42095 or < 9.0.0.4.386

CVE-2023-39239 HIGH
7.2 Sep 07

It is identified a format string vulnerability in ASUS RT-AX56U V2’s General function API. Rated high severity (CVSS 7.2

CVE-2023-39238 HIGH
7.2 Sep 07

It is identified a format string vulnerability in ASUS RT-AX56U V2. Rated high severity (CVSS 7.2), this vulnerability i

CVE-2021-37910 MEDIUM
5.3 Nov 12

ASUS routers Wi-Fi protected access protocol (WPA2 and WPA3-SAE) has improper control of Interaction frequency vulnerabi

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