CVE-2026-6241 Overview
CVE-2026-6241 is an authenticated format string vulnerability [CWE-134] affecting the ONVIF AddScopes operation in the TP-Link Tapo C520WS v2 network camera. The flaw stems from user-controlled input being passed to formatting functions without adequate sanitization. An authenticated attacker on an adjacent network can inject format specifiers into ONVIF scope parameters to manipulate memory handling behavior. Successful exploitation crashes the ONVIF management service, producing a denial-of-service (DoS) condition that disrupts normal camera operation.
Critical Impact
An authenticated adjacent-network attacker can crash the ONVIF management service on the Tapo C520WS v2, disrupting video surveillance and remote management functionality.
Affected Products
- TP-Link Tapo C520WS v2 network camera
- ONVIF management service on affected firmware versions
- Deployments exposing ONVIF endpoints on local or adjacent networks
Discovery Timeline
- 2026-06-06 - CVE-2026-6241 published to NVD
- 2026-06-08 - Last updated in NVD database
Technical Details for CVE-2026-6241
Vulnerability Analysis
The vulnerability resides in the ONVIF (Open Network Video Interface Forum) AddScopes operation, a SOAP-based method used to add scope parameters that describe device capabilities and metadata. The Tapo C520WS v2 firmware forwards attacker-supplied scope strings into C-style formatting functions such as printf, sprintf, or logging wrappers without first stripping or escaping format conversion specifiers. When the resulting string contains tokens like %s, %x, or %n, the formatting function interprets them as directives and reads or writes memory locations that were never intended to be exposed to attacker control.
In this implementation, the impact is limited to memory corruption that crashes the ONVIF service, producing a denial-of-service condition. Because authentication is required and the vulnerability is reachable only from an adjacent network, mass exploitation is unlikely. However, in shared corporate or multi-tenant environments where ONVIF credentials are widely distributed, abuse remains practical.
Root Cause
The root cause is improper handling of externally-influenced input within a format string [CWE-134]. The ONVIF service treats the scope value provided by the SOAP client as a format string rather than as data, violating the standard practice of using a fixed format specifier such as "%s" paired with the untrusted argument.
Attack Vector
An attacker authenticates to the ONVIF endpoint exposed by the Tapo C520WS v2 over the local or adjacent network. The attacker then issues an AddScopes SOAP request whose Scopes element contains crafted format specifiers. When the camera firmware passes the value to its internal logging or formatting routine, the specifiers trigger invalid memory accesses, terminating the ONVIF service and breaking remote video management until the device or service restarts.
No verified public proof-of-concept code is available. Refer to the TP-Link FAQ on Tapo C520WS for vendor guidance.
Detection Methods for CVE-2026-6241
Indicators of Compromise
- Repeated ONVIF AddScopes SOAP requests containing format specifiers such as %s, %x, %p, or %n in the Scopes element.
- Unexpected restarts or crash logs from the ONVIF management service on Tapo C520WS v2 devices.
- Loss of ONVIF discovery, PTZ, or streaming functionality while the underlying RTSP stream remains active.
Detection Strategies
- Inspect SOAP traffic to TCP ports used by ONVIF (commonly 2020, 8080, or 80) for AddScopes requests containing % conversion characters in scope URIs.
- Correlate authentication events on the camera with subsequent ONVIF service crashes to identify abusive accounts.
- Baseline the rate of AddScopes invocations; legitimate use is rare and configuration-driven, so spikes warrant investigation.
Monitoring Recommendations
- Forward camera syslog and ONVIF service logs to a centralized SIEM and alert on repeated service termination events.
- Monitor network segments hosting IP cameras for unauthorized hosts initiating ONVIF SOAP sessions.
- Track firmware versions across the IoT inventory to confirm patched builds are deployed.
How to Mitigate CVE-2026-6241
Immediate Actions Required
- Apply the latest firmware for the Tapo C520WS v2 as listed in the TP-Link Firmware Release Notes.
- Rotate ONVIF account credentials and remove unused accounts on affected cameras.
- Restrict ONVIF access to a dedicated management VLAN that excludes general user devices.
Patch Information
TP-Link addresses the issue in firmware updates published on the Tapo C520WS v2 product page. Review the TP-Link Firmware Release Notes for the fixed version applicable to your regional firmware track, and validate the running build using the camera's web management interface or the Tapo mobile application.
Workarounds
- Disable ONVIF on cameras that do not require third-party Video Management System integration.
- Apply ACLs or firewall rules to permit ONVIF SOAP traffic only from trusted management hosts.
- Use strong, unique ONVIF credentials and disable shared service accounts to limit which authenticated users can reach AddScopes.
# Example: restrict ONVIF access to a single management host using iptables on an upstream gateway
iptables -A FORWARD -p tcp -s 192.0.2.10 -d 192.0.2.50 --dport 2020 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.0.2.50 --dport 2020 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
