CVE-2026-76852: Netcore NR268 Auth Bypass Vulnerability

CVE-2026-76852 Overview

CVE-2026-76852 is a firmware integrity verification flaw affecting Netcore NR268 routers running firmware version 1.7.121109. The vulnerability resides in the mtd_write component, which fails to properly validate firmware authenticity. Attackers with low-privileged network access can leverage put_file.cgi and logic in check_image_uuid.c to forge signature checks and load unauthorized firmware images. Successful exploitation compromises the confidentiality, integrity, and availability of the device. The weakness is categorized under CWE-354: Improper Validation of Integrity Check Value.

Critical Impact

A remote authenticated attacker can install forged firmware on Netcore NR268 devices, enabling persistent implantation and full device takeover.

Affected Products

• Netcore NR268 router
• Firmware version 1.7.121109
• Components: mtd_write, put_file.cgi, check_image_uuid.c

Discovery Timeline

• 2026-09-15 - CVE-2026-76852 published to the National Vulnerability Database (NVD)
• 2026-09-17 - Last updated in NVD database

Technical Details for CVE-2026-76852

Vulnerability Analysis

The flaw is a firmware integrity verification failure in the Netcore NR268 update path. The mtd_write routine writes firmware images to flash without cryptographically validating the origin of the image. The authenticity check relies on values that an attacker can generate or replay, breaking the trust boundary between vendor-signed firmware and attacker-supplied images.

An authenticated attacker submits a crafted firmware payload through put_file.cgi. The routine invoked by check_image_uuid.c compares identifiers rather than verifying a cryptographic signature over the image contents. Because these identifiers travel with the image itself, they can be forged to match expected values.

Once the forged image passes the check, mtd_write commits the payload to flash. The device then boots attacker-controlled firmware, allowing implantation of backdoors, credential theft, or use of the router as a pivot into internal networks.

Root Cause

The root cause is an improper integrity check (CWE-354). The update pipeline substitutes an identifier comparison for a signature verification step. No trusted key material anchors the check, so integrity is asserted rather than proven.

Attack Vector

Exploitation requires network access to the device management interface and low-level credentials. The attacker uploads a modified firmware image via put_file.cgi, ensures the UUID fields match those inspected by check_image_uuid.c, and triggers the flash-write path. User interaction is not required.

Refer to the GitHub firmware forgery documentation and the VulnCheck advisory for technical exploitation notes.

Detection Methods for CVE-2026-76852

Indicators of Compromise

• Unexpected HTTP POST requests to put_file.cgi on the router management interface
• Firmware version strings or build identifiers that do not match vendor-issued releases
• Unscheduled reboots or MTD partition writes recorded in device logs
• Outbound connections from the router to unknown command-and-control infrastructure

Detection Strategies

• Monitor administrative interfaces of NR268 devices for authenticated firmware upload activity outside change windows
• Compare running firmware hashes against a known-good vendor manifest on a scheduled basis
• Inspect network traffic for anomalous management sessions originating from non-administrative subnets

Monitoring Recommendations

• Forward router syslog and management-plane logs to a centralized SIEM for correlation
• Alert on repeated authentication attempts against the NR268 web interface followed by firmware operations
• Track device uptime and firmware version drift across the router fleet to identify silent reflashing

How to Mitigate CVE-2026-76852

Immediate Actions Required

• Restrict access to the NR268 management interface to trusted administrative subnets only
• Rotate all router administrative credentials and disable default or shared accounts
• Audit currently deployed firmware images against vendor-published hashes
• Isolate NR268 devices from sensitive network segments until a vendor fix is validated

Patch Information

No vendor patch has been referenced in the published advisories at the time of NVD publication. Consult the VulnCheck advisory for updates on remediation availability from Netcore.

Workarounds

• Block access to put_file.cgi at the network perimeter and via device ACLs where supported
• Disable remote management on WAN interfaces and require VPN access for administration
• Replace vulnerable NR268 units with devices that enforce signed firmware updates when replacement is feasible
• Continuously validate firmware integrity through out-of-band inspection until a signed update mechanism is available

# Example firewall rule to restrict management access to the NR268
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