CVE-2025-12259 Overview
CVE-2025-12259 is a stack-based buffer overflow vulnerability in the TOTOLINK A3300R router running firmware version 17.0.0cu.557_B20221024. The flaw resides in the setScheduleCfg function within /cgi-bin/cstecgi.cgi, where the recHour POST parameter is not properly bounded before being copied to a fixed-size stack buffer. Attackers can trigger the overflow remotely over the network with low-privilege credentials, with no user interaction required. Public disclosure includes documentation of the affected request path, and the issue is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Critical Impact
Remote attackers can corrupt stack memory on the router, leading to denial of service or potential arbitrary code execution on the embedded device.
Affected Products
- TOTOLINK A3300R router (hardware)
- TOTOLINK A3300R firmware version 17.0.0cu.557_B20221024
- POST parameter handler in /cgi-bin/cstecgi.cgi
Discovery Timeline
- 2025-10-27 - CVE-2025-12259 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-12259
Vulnerability Analysis
The vulnerability exists in the setScheduleCfg handler exposed through the CGI endpoint /cgi-bin/cstecgi.cgi. The handler accepts a JSON or form-encoded POST body containing scheduling parameters. The recHour argument is copied into a stack-allocated buffer without length validation, allowing an attacker to overwrite adjacent stack memory, including the saved return address. Because the device runs the CGI process with elevated privileges typical of embedded Linux router firmware, successful exploitation can lead to control-flow hijack. Technical documentation of the request path is published in the GitHub vulnerability writeup and tracked as VulDB ID #329930.
Root Cause
The root cause is missing bounds checking on attacker-controlled input copied into a fixed-size stack buffer. The setScheduleCfg function uses an unsafe string copy on the recHour parameter, which the attacker fully controls through the HTTP POST body. No length validation, canary check, or input sanitization is applied before the copy, so an oversized value writes past the buffer boundary into the saved frame pointer and return address on the call stack.
Attack Vector
An attacker sends a crafted HTTP POST request to /cgi-bin/cstecgi.cgi targeting the setScheduleCfg action with an oversized recHour value. Authentication at a low privilege level is required, but no user interaction is needed. The attack is network-reachable, so any exposure of the router management interface to untrusted networks materially increases risk. Successful exploitation can corrupt the call stack of the CGI process and, depending on memory protections present in the firmware build, redirect execution to attacker-controlled instructions or shellcode delivered in the same request body.
No verified proof-of-concept code is included in this advisory. Refer to the GitHub writeup for the request structure used to reach the vulnerable function.
Detection Methods for CVE-2025-12259
Indicators of Compromise
- HTTP POST requests to /cgi-bin/cstecgi.cgi containing the setScheduleCfg action and an unusually long recHour value.
- Unexpected reboots, crashes, or watchdog resets of the TOTOLINK A3300R coinciding with inbound web management traffic.
- New or unexplained outbound connections originating from the router to unfamiliar hosts after receipt of a malformed schedule configuration request.
Detection Strategies
- Inspect web server and CGI logs on the router for setScheduleCfg requests where the recHour field length exceeds expected hour-value semantics (typically 1–2 bytes).
- Deploy network IDS signatures that flag POST bodies to /cgi-bin/cstecgi.cgi containing oversized parameter values or non-numeric data in numeric scheduling fields.
- Correlate router crash telemetry, SNMP traps, or syslog reboot events with preceding HTTP requests to the management interface.
Monitoring Recommendations
- Forward router syslog and authentication events to a centralized log platform and alert on repeated CGI requests from a single source.
- Monitor management-plane access for sessions originating from outside trusted administrative subnets.
- Track firmware version inventory to identify any A3300R units still running 17.0.0cu.557_B20221024.
How to Mitigate CVE-2025-12259
Immediate Actions Required
- Restrict access to the TOTOLINK A3300R web management interface to trusted management VLANs only and block it from the WAN.
- Rotate all router administrative credentials, since exploitation requires only low-privilege authenticated access.
- Audit existing scheduled configurations for unexpected entries that may indicate prior exploitation attempts.
Patch Information
No vendor advisory or patched firmware release has been published in the references associated with CVE-2025-12259. Consult the TOTOLINK official website for firmware updates and check whether a newer firmware build supersedes 17.0.0cu.557_B20221024. Until a fixed firmware is available, treat the device as vulnerable and apply compensating controls.
Workarounds
- Disable remote (WAN-side) administration on the A3300R and require management access through a VPN or jump host.
- Place the router behind an upstream firewall that drops inbound traffic to TCP ports hosting /cgi-bin/cstecgi.cgi.
- Where feasible, replace the affected device with hardware that receives active vendor security maintenance.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
