CVE-2025-9781 Overview
CVE-2025-9781 is a buffer overflow vulnerability in the TOTOLINK A702R router running firmware version 4.0.0-B20211108.1423. The flaw resides in the sub_4162DC function of the /boafrm/formFilter endpoint. Attackers can trigger the overflow by manipulating the ip6addr argument, corrupting adjacent memory on the device. The attack is launchable over the network and requires only low-level privileges. Public exploit details have been disclosed, increasing the risk of opportunistic abuse against exposed devices. The weakness is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Critical Impact
Remote attackers can corrupt router memory through the ip6addr parameter, potentially leading to denial of service or arbitrary code execution on the embedded device.
Affected Products
- TOTOLINK A702R router (hardware)
- TOTOLINK A702R firmware 4.0.0-B20211108.1423
- Deployments exposing the /boafrm/formFilter web interface
Discovery Timeline
- 2025-09-01 - CVE-2025-9781 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-9781
Vulnerability Analysis
The vulnerability exists in the TOTOLINK A702R firmware web management interface. The sub_4162DC function handles requests to /boafrm/formFilter, which processes IPv6 filtering configuration. The function reads the ip6addr HTTP parameter and writes it into a fixed-size stack or heap buffer without bounds checking. When an oversized value is supplied, the copy operation overruns the buffer and overwrites adjacent memory.
This class of flaw, [CWE-119], commonly enables denial of service through process corruption. On embedded MIPS or ARM router firmware, attackers may also achieve code execution by overwriting return addresses or function pointers. The boafrm binary typically runs with root privileges on TOTOLINK devices, so successful exploitation grants control over the router.
Root Cause
The root cause is missing input length validation on the ip6addr parameter inside sub_4162DC. The function trusts the caller-supplied string and copies it directly into a fixed-size buffer. There is no upper-bound check, no use of size-limited string functions, and no sanitization of the IPv6 address format before the copy.
Attack Vector
An attacker with access to the router's HTTP management interface and valid low-privilege credentials sends a crafted POST request to /boafrm/formFilter. The request includes an ip6addr field populated with an oversized payload designed to overflow the destination buffer. The attack requires no user interaction. Publicly available proof-of-concept material documents the parameter and request structure. See the GitHub PoC Documentation for the exact request layout.
Detection Methods for CVE-2025-9781
Indicators of Compromise
- HTTP POST requests to /boafrm/formFilter containing abnormally long ip6addr parameter values
- Router reboots, web interface crashes, or boafrm process restarts immediately following filter configuration requests
- Unexpected outbound connections originating from the router management plane following inbound HTTP activity
- New or modified firewall and filter rules that were not configured by administrators
Detection Strategies
- Inspect HTTP request bodies destined for the router admin interface and flag ip6addr values exceeding valid IPv6 address length (39 characters)
- Deploy network IDS signatures matching POST requests to /boafrm/formFilter with non-conforming IPv6 payloads
- Correlate router syslog entries showing boafrm segmentation faults with preceding HTTP requests from the same source
- Monitor for management interface access from non-administrative network segments
Monitoring Recommendations
- Forward router system logs to a centralized logging platform and alert on boafrm crash signatures
- Track authentication events on the router web interface for brute-force activity that precedes exploitation
- Baseline normal request sizes to /boafrm/* endpoints and alert on deviations
- Review VulDB records VulDB #322083 Details for additional indicators
How to Mitigate CVE-2025-9781
Immediate Actions Required
- Restrict access to the router web management interface to trusted internal networks only, and disable remote WAN administration
- Change default and weak administrative credentials to reduce the impact of the low-privilege requirement for exploitation
- Segment vulnerable TOTOLINK A702R devices away from sensitive network zones until a firmware update is available
- Monitor the TOTOLINK Official Website for vendor security advisories and firmware releases
Patch Information
At the time of publication, no vendor patch has been referenced in the advisory data for CVE-2025-9781. Administrators should track the VulDB #322083 Incident record and the vendor support channels for firmware updates that address the sub_4162DC bounds-checking flaw. Replacement of end-of-life TOTOLINK A702R hardware should be considered if no fix is released.
Workarounds
- Block external access to TCP ports serving the router HTTP management interface at the network perimeter
- Apply upstream ACLs that drop POST requests to /boafrm/formFilter from untrusted sources
- Disable IPv6 filtering configuration features in the admin UI if not required by the deployment
- Place affected routers behind a reverse proxy or WAF that enforces parameter length limits on ip6addr
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
