# CVE-2026-76870: Netcore NR255-V out-of-bounds read in firmware upload validation

Source: https://junglewise.ai/threats/cve-2026-76870-netcore-nr255-v-out-of-bounds-read-in-firmware-upload-validation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-15. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-76870 · Severity: high · CVSS 7.1 · Published 2026-09-15

The Netcore NR255-V is a wireless router used in residential and small business networks. This vulnerability allows an authenticated attacker to upload a truncated firmware image, causing the device to read beyond allocated memory boundaries during validation. A successful exploit could lead to information disclosure or unexpected device behavior, potentially disrupting network connectivity.

Technologies: [Netcore NR255-V](https://junglewise.ai/threats/technologies/nr255-v). Vendors: [Netcore](https://junglewise.ai/threats/vendors/netcore).

## Quick answers

**Is CVE-2026-76870 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-76870 being exploited in the wild.

**How severe is CVE-2026-76870?** High severity, with a CVSS score of 7.1, published 15 September 2026.

**Which products and versions are affected?** Netcore NR255-V 1.5.130703.

**Is there a fix for CVE-2026-76870?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-76870 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-76870?** Check whether you run Netcore NR255-V at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This is an out-of-bounds read (CWE-125) vulnerability in the mtd_write pre-flash validation routine of the Netcore NR255-V firmware. The vulnerability is triggered when a truncated firmware image is uploaded via the put_file_cgi.c interface, causing out-of-bounds memory reads across multiple validation components (main.c, check_image_uuid.c, and oemMD5Update.c). The attack requires network access and authentication (PR:L per CVSS vector), with no user interaction needed. An attacker can achieve information disclosure and potentially cause availability impact by inducing invalid device behavior. Patches or fixes for this vulnerability are not mentioned in available sources.

## Affected products

- Netcore NR255-V 1.5.130703

## Timeline

- 2026-09-04: disclosed: Vulnerability publicly disclosed on GitHub
- 2026-09-15: advisory: CVE-2026-76870 published and advisory released

## References

- [https://github.com/draw-ctf/netcore-router-public-refs/blob/main/2026.08.19-netcore-nr255v-firmware-upload-oob.md](https://github.com/draw-ctf/netcore-router-public-refs/blob/main/2026.08.19-netcore-nr255v-firmware-upload-oob.md)
- [https://www.vulncheck.com/advisories/netcore-nr255-v-1.5.130703-out-of-bounds-read-in-mtd-write-firmware-upload-validation](https://www.vulncheck.com/advisories/netcore-nr255-v-1.5.130703-out-of-bounds-read-in-mtd-write-firmware-upload-validation)

## Related threats

- [Netcore NR255-V stored cross-site scripting in L7 content management](https://junglewise.ai/threats/cve-2026-92257-netcore-nr255-v-stored-cross-site-scripting-in-l7-content)
- [Netcore NR255-V sensitive information disclosure in VPN configuration handlers](https://junglewise.ai/threats/cve-2026-92256-netcore-nr255-v-sensitive-information-disclosure-in-vpn)
- [Netcore NR255-V out-of-bounds read in filter_arp_put_file.cgi](https://junglewise.ai/threats/cve-2026-92255-netcore-nr255-v-out-of-bounds-read-in-filter-arp-put-file-cgi)
- [Netcore NR255-V stored cross-site scripting in DHCP and ARP hostname fields](https://junglewise.ai/threats/cve-2026-76873-netcore-nr255-v-stored-cross-site-scripting-in-dhcp-and-arp)
- [Netcore NR255-V stored cross-site scripting in DHCP and ACL management](https://junglewise.ai/threats/cve-2026-76872-netcore-nr255-v-stored-cross-site-scripting-in-dhcp-and-acl)