CVE-2026-7546 Overview
CVE-2026-7546 is a stack-based buffer overflow in the Totolink NR1800X router running firmware version 9.1.0u.6279_B20210910. The flaw resides in the find_host_ip function within the lighttpd web server component. Attackers manipulate the HTTP Host header to overflow a fixed-size stack buffer. The vulnerability is reachable over the network without authentication or user interaction. Public exploit details have been disclosed, increasing the risk of opportunistic attacks against exposed devices. The issue is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Critical Impact
Unauthenticated remote attackers can corrupt the lighttpd process stack on Totolink NR1800X routers, enabling code execution or full device compromise through a crafted HTTP Host header.
Affected Products
- Totolink NR1800X firmware 9.1.0u.6279_B20210910
- lighttpd web server component shipped with the affected firmware
- The find_host_ip function processing the HTTP Host header
Discovery Timeline
- 2026-05-01 - CVE-2026-7546 published to NVD
- 2026-05-01 - Last updated in NVD database
Technical Details for CVE-2026-7546
Vulnerability Analysis
The vulnerability exists in the find_host_ip function of the lighttpd HTTP daemon embedded in Totolink NR1800X firmware. The function parses the HTTP Host header from incoming requests but fails to validate the length of the supplied value before copying it into a fixed-size stack buffer. An attacker who sends a crafted HTTP request with an oversized Host header overflows adjacent stack memory. The overflow can corrupt saved return addresses and local variables, leading to control-flow hijacking or process termination. Because lighttpd runs with elevated privileges on the device, successful exploitation grants the attacker control over the router's web management plane.
Root Cause
The root cause is the absence of bounds checking on attacker-controlled HTTP header data inside find_host_ip. The function relies on unsafe string handling against a stack-allocated buffer without enforcing a maximum length. This pattern matches [CWE-119] and is common in embedded HTTP parsers compiled without modern stack protections. Refer to the GitHub CVE Documentation for the published technical breakdown.
Attack Vector
Exploitation requires only network reachability to the router's HTTP management interface. An attacker sends an HTTP request containing an oversized Host header value to the device. No credentials, prior session, or victim interaction are required. Devices that expose the web interface to the WAN are at the highest risk, while LAN-side exposure remains exploitable by adversaries who already have local network access. Additional vulnerability metadata is available in the VulDB Vulnerability #360357 entry.
No verified exploit code has been published in the enriched data. The disclosure references the crafted HTTP Host header as the trigger, with the overflow occurring inside find_host_ip during request parsing.
Detection Methods for CVE-2026-7546
Indicators of Compromise
- HTTP requests targeting the router's web interface containing abnormally long Host header values, often exceeding several hundred bytes.
- lighttpd process crashes, restarts, or watchdog reboots correlated with inbound HTTP traffic.
- Outbound connections from the router to unfamiliar hosts following anomalous HTTP requests, suggesting post-exploit activity.
Detection Strategies
- Inspect HTTP traffic to management interfaces and alert on Host headers that exceed RFC-typical lengths or contain non-printable bytes.
- Deploy network IDS signatures that flag oversized or malformed HTTP headers directed at embedded device IP ranges.
- Correlate router syslog or remote logging events for repeated lighttpd segmentation faults with originating source IPs.
Monitoring Recommendations
- Forward router logs to a centralized logging or SIEM platform and baseline normal HTTP header sizes for management endpoints.
- Monitor for new or unexpected listening services on affected routers, which may indicate post-exploitation persistence.
- Track WAN-side scanning activity targeting TCP ports used by the device's web management interface.
How to Mitigate CVE-2026-7546
Immediate Actions Required
- Disable WAN-side access to the router's HTTP management interface and restrict administration to trusted LAN segments only.
- Place affected Totolink NR1800X devices behind a network segment that filters inbound HTTP traffic from untrusted sources.
- Audit device inventories for firmware version 9.1.0u.6279_B20210910 and prioritize replacement or isolation where no patch is available.
Patch Information
No vendor patch is referenced in the enriched CVE data at the time of publication. Administrators should monitor the Totolink Official Site for firmware updates addressing the find_host_ip overflow. Until a fix is released, compensating controls remain the only mitigation.
Workarounds
- Block inbound TCP connections to the router's HTTP management port from untrusted networks at an upstream firewall.
- Apply ACLs that restrict the management interface to specific administrative source IP addresses.
- Replace internet-exposed NR1800X devices with patched hardware where firmware updates remain unavailable.
# Example upstream firewall rule restricting router HTTP management access
# Replace 192.0.2.10 with the trusted admin host and 198.51.100.5 with the router
iptables -A FORWARD -p tcp -d 198.51.100.5 --dport 80 -s 192.0.2.10 -j ACCEPT
iptables -A FORWARD -p tcp -d 198.51.100.5 --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
