CVE-2021-35395

The Realtek Jungle SDK (v2.x up to v3.4.14B) ships an HTTP management web server, in both Go-Ahead ('webs') and Boa ('boa') variants, containing multiple stack buffer overflows in form handlers such as formRebootCheck, formWsc, formWlanMultipleAP, formWlSiteSurvey and formStaticDHCP, plus arbitrary command execution/injection flaws in formSysCmd and formWsc. An unauthenticated attacker triggers these by sending crafted HTTP requests with oversized submit-url, ifname, hostname or peerPin parameters, or by injecting commands via the sysCmd or peerPin parameters. Successful exploitation yields arbitrary code execution on the device, typically giving the attacker full control of the affected router, access point or IoT device. Any device whose vendor embedded the affected SDK is exposed, with public reporting linking the flaws to roughly 65 downstream vendors and nearly a million internet-visible devices. Exploitation is confirmed in the wild: the issue is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03), and researchers observed Mirai botnet variants and other attackers compromising Realtek-based devices; ransomware use is unknown.

What to do: Apply firmware updates from your device vendor incorporating a patched Realtek SDK (newer than v3.4.14B), per CISA's required action; since vendors ship modified builds, confirm with the manufacturer that your model is fixed. Until patched, disable remote/web-based administration or restrict the management interface (WAN-facing HTTP) with a firewall so it is not internet-exposed. Defenders should also monitor Realtek-based devices for botnet-style activity (e.g., Mirai-variant traffic), as a public PoC/advisory from IoT Inspector is available and exploitation is ongoing.