Compromised DVR/NVR devices fuel Telnet scanning in Japan
JPCERT observed increased Telnet scanning from compromised DVR/NVR devices in Japan during Q4 2025, with many running outdated firmware containing known vulnerabilities.
Sourceblogs.jpcert.or.jp — open the original
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JPCERT's TSUBAME sensor network detected a temporary spike in Telnet traffic (23/TCP) originating from Japan in October 2025, followed by a decline starting November 7. Analysis revealed that up to 80% of this traffic on certain days originated from specific groups of DVR/NVR devices. Many of these devices displayed login screens with outdated copyright notices (e.g., 2014), indicating prolonged periods without firmware updates and likely exposure to known vulnerabilities.
Comparative analysis between Japanese and overseas sensors showed that overseas sensors received higher packet volumes overall, with a gradual upward trend observed from October onward in both domestic and international networks. Cross-regional sensor comparison revealed consistent scanning activity targeting common protocols including SSH (22/TCP), Telnet (23/TCP), HTTP (80/TCP), HTTPS (443/TCP), and HTTP-alt (8080/TCP) across Japan, North America, Europe, and other regions.
The findings underscore the persistent security risk posed by legacy IoT devices, particularly DVR/NVR systems, that remain internet-accessible despite running obsolete firmware. Organizations operating similar devices should verify their exposure and implement timely firmware updates to mitigate exploitation risks.
Source reporting: https://blogs.jpcert.or.jp/en/2026/05/tsubame_overflow_2025-10-12.html
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