Netcore NR256CN: Pre-authentication stack overflow in Boa web server
Summary
The Boa web server of the Netcore NR256CN router contains a stack buffer overflow in the user_ok() function, which processes HTTP Basic authentication usernames. An unauthenticated attacker can send a username longer than 63 bytes to a protected /router/*.cgi route, which can crash the web server process and potentially allow code execution. The vulnerability is reachable without credentials, so exposure of the management interface is the decisive factor.
Affected
- Netcore NR256CN firmware through 1.5.140116
- Lower bound of the affected range not confirmed
Fixed in
Unknown. No vendor advisory or patched firmware has been confirmed.
Workaround
- Block WAN access to the web and management interface with strict firewall rules
- Monitor for unexpected crashes or restarts of the Boa process
Exploitation
- No confirmed exploitation in the wild found
- A public write-up exists; proof-of-concept details are withheld by the publisher
- CISA SSVC: exploitation none, automatable yes, total technical impact
Our recommendation
- Inventory all NR256CN devices and their firmware versions
- Remove any WAN exposure of the web or management interface and verify this from outside your network
- Contact Netcore or your reseller for a fixed firmware build for this CVE and the related CVE-2026-111712 and CVE-2026-112016
- Monitor for Boa process crashes and re-check NVD and the vendor advisory once published
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub write-up (lukadqq/netcore-router-public-refs) github.com
- VulnCheck advisory www.vulncheck.com
- VulDB CVE-2026-111711 vuldb.com
- Strix CVE-2026-111711 www.strix.ai
- Positive Technologies PT-2026-116110 (Vulners) vulners.com
- The Hacker Wire CVE-2026-111711 www.thehackerwire.com
- CVE Brief archive 2026/10/17 cvebrief.com
- Strix CVE-2026-112016 www.strix.ai
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 01:22.
Original description (NVD)
Netcore NR256CN through 1.5.140116 contains a pre-authentication stack overflow vulnerability in the Boa web server's user_ok() function, which copies Basic-auth usernames with unbounded strcpy() calls into 64-byte stack buffers. Unauthenticated attackers can send a username longer than 63 bytes to any protected /router/*.cgi route to crash the main Boa process or potentially execute code.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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