CVE-2026-76853 Overview
CVE-2026-76853 is a security check bypass vulnerability in the Netcore NR268 router running firmware version 1.7.121109. The flaw resides in the parame_put_file.cgi handler, where the restore archive prefix validation logic in put_parame_file_cgi.c fails to properly enforce restrictions. Authenticated attackers can craft archives that bypass the prefix check and manipulate restore operations on the device. The vulnerability is tracked under CWE-353 (Missing Support for Integrity Check).
Critical Impact
Attackers with low-privilege network access can bypass restore archive validation to compromise router integrity and availability without user interaction.
Affected Products
- Netcore NR268 router
- Firmware version 1.7.121109
- parame_put_file.cgi component (put_parame_file_cgi.c)
Discovery Timeline
- 2026-09-15 - CVE-2026-76853 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-76853
Vulnerability Analysis
The Netcore NR268 exposes a restore functionality through the parame_put_file.cgi endpoint. This CGI handler accepts configuration archives and validates them by inspecting a prefix before applying the restore. The validation logic in put_parame_file_cgi.c implements the prefix check in a way that can be bypassed by a crafted archive header. Because the check is the sole integrity gate for restore operations, bypassing it allows an attacker to submit restore payloads that the firmware would otherwise reject. Successful exploitation grants the attacker meaningful influence over router state, impacting configuration integrity and device availability.
Root Cause
The root cause is missing support for integrity verification [CWE-353] within the restore archive handler. The prefix comparison in put_parame_file_cgi.c does not adequately validate the full structure or authenticity of the uploaded archive. It relies on a superficial string match that attackers can satisfy while still delivering unintended contents. No cryptographic integrity check accompanies the prefix validation.
Attack Vector
Exploitation requires network access to the router's management interface and authenticated access with low privileges. No user interaction is needed. An attacker submits a specially crafted restore archive whose header satisfies the flawed prefix check in parame_put_file.cgi. The handler accepts the archive and proceeds with restore processing, allowing the attacker to influence device configuration and operation.
No verified public exploit code is available for this CVE. Full technical details on the bypass technique are documented in the GitHub Bypass Documentation and the VulnCheck Security Advisory.
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Stop Identity AttacksDetection Methods for CVE-2026-76853
Indicators of Compromise
- Unexpected HTTP POST requests to parame_put_file.cgi on the router management interface
- Router configuration changes that do not correspond to administrator activity
- Restore operations logged outside of scheduled maintenance windows
- Unusual outbound traffic from the router following a restore event
Detection Strategies
- Monitor router web-management logs for calls to parame_put_file.cgi and correlate with authenticated administrator sessions
- Alert on any successful restore operation that was not initiated through a documented change process
- Track baseline configuration hashes and flag divergence following restore activity
Monitoring Recommendations
- Forward router syslog data to a centralized logging or SIEM platform for analysis
- Enable authentication logging on the router and monitor for low-privilege accounts issuing restore requests
- Inspect network flows to management interfaces for anomalies from non-administrative subnets
How to Mitigate CVE-2026-76853
Immediate Actions Required
- Restrict access to the NR268 web-management interface to trusted administrative networks only
- Disable remote management on WAN interfaces where operationally feasible
- Rotate administrative credentials and remove unused low-privilege accounts that could reach parame_put_file.cgi
- Review recent restore operations for unauthorized activity
Patch Information
At the time of publication, no vendor patch is referenced in the NVD entry for firmware version 1.7.121109. Administrators should consult the VulnCheck Security Advisory for the current remediation status and monitor Netcore for firmware updates addressing the prefix validation logic in put_parame_file_cgi.c.
Workarounds
- Place the router management interface behind a VPN or jump host to eliminate direct network exposure
- Apply firewall rules that block untrusted sources from reaching HTTP/HTTPS management ports
- Enforce strong, unique credentials for every account permitted to invoke restore functionality
- Regularly export and verify a known-good configuration backup to detect unauthorized restores
# Example: restrict router management access to a trusted subnet
iptables -A INPUT -p tcp --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
