CVE-2026-76862 Overview
CVE-2026-76862 is an OS command argument injection vulnerability [CWE-88] in Netcore NR255-V routers running firmware version 1.5.130703. The flaw resides in the Nettools tcpdump launch paths, specifically the ntools_start_set_cgi, ntools_tcpdump_start_set_cgi, exe_default, and ntools_proc components. Authenticated attackers can inject crafted arguments into the tcpdump invocation to manipulate executed system commands on the device.
Critical Impact
Successful exploitation lets an attacker with low privileges alter tcpdump command arguments to run attacker-controlled operations against the router, resulting in high confidentiality, integrity, and availability impact.
Affected Products
- Netcore NR255-V router
- Firmware version 1.5.130703
- Nettools tcpdump launch components: ntools_start_set_cgi, ntools_tcpdump_start_set_cgi, exe_default, ntools_proc
Discovery Timeline
- 2026-09-15 - CVE-2026-76862 published to NVD
- 2026-09-17 - Last updated in NVD database
Technical Details for CVE-2026-76862
Vulnerability Analysis
The vulnerability is an argument injection issue [CWE-88] in the Nettools diagnostic feature that wraps the tcpdump utility. The CGI handlers ntools_start_set_cgi and ntools_tcpdump_start_set_cgi accept user-supplied parameters that are passed as arguments to the tcpdump process launched by exe_default and ntools_proc. Because the handlers do not restrict argument prefixes or dangerous tcpdump flags, an attacker can inject additional command-line options that change what tcpdump does at runtime.
tcpdump supports flags such as -z (post-rotate command) and -w (write output to a file) that can be abused to execute arbitrary programs or write attacker-controlled files. By manipulating the argument stream reaching tcpdump, an attacker can leverage these flags to run commands on the router with the privileges of the tcpdump process. The attack requires only network access and low-privilege authentication to the web interface.
Root Cause
The root cause is missing argument sanitization in the Nettools tcpdump launch paths. User input flows from the CGI endpoints into command construction routines without validation of leading dashes or disallowed tcpdump options. The affected components trust the caller to supply benign values, violating the safe-argument construction pattern for external process execution.
Attack Vector
An authenticated attacker sends crafted HTTP requests to the vulnerable CGI endpoints on the router management interface. The injected argument values are appended to the tcpdump command line by exe_default or ntools_proc, which then spawns tcpdump with the attacker-controlled flags. See the GitHub advisory and the VulnCheck advisory for endpoint-level technical details.
Detection Methods for CVE-2026-76862
Indicators of Compromise
- Unexpected tcpdump processes running on the router with command lines containing -z, -w, or other execution-related flags
- HTTP POST requests to ntools_start_set_cgi or ntools_tcpdump_start_set_cgi containing dashes or shell metacharacters in parameter values
- Presence of new or modified files in tcpdump-writable directories on the device
- Outbound network connections from the router to unfamiliar hosts following diagnostic tool invocation
Detection Strategies
- Inspect router management HTTP logs for parameter values that begin with - reaching the Nettools CGI endpoints
- Monitor process execution telemetry for tcpdump invocations with unusual flag combinations or unexpected output paths
- Correlate authentication events with subsequent diagnostic tool activity to identify low-privilege accounts pivoting to command execution
Monitoring Recommendations
- Forward router syslog and web interface access logs to a centralized log platform for retention and query
- Alert on any non-administrative account invoking Nettools diagnostic features
- Baseline normal tcpdump usage on managed routers and flag deviations in argument patterns
How to Mitigate CVE-2026-76862
Immediate Actions Required
- Restrict access to the router management interface to trusted management networks only
- Rotate credentials for all accounts with access to the Nettools diagnostic features
- Disable remote WAN-side management if enabled on affected NR255-V devices
- Review router logs for prior use of the vulnerable CGI endpoints and evidence of argument injection
Patch Information
At the time of publication, no vendor patch is referenced in the available advisories. Consult the VulnCheck advisory and the Netcore vendor site for firmware updates addressing 1.5.130703.
Workarounds
- Block access to ntools_start_set_cgi and ntools_tcpdump_start_set_cgi at an upstream network device where feasible
- Limit web management access using source IP allowlists on the router
- Reduce the number of low-privilege accounts able to authenticate to the router web interface
- Segment affected routers away from sensitive internal networks until a firmware fix is available
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.