---
id: "CVE-2021-35395"
kind: "vulnerability"
aliases: ["CVE-2021-35395"]
title: "Realtek AP-Router SDK: Realtek AP-Router SDK Buffer Overflow Vulnerability"
severity: "critical"
cvss: 10.0
epss: 0.981
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Realtek AP-Router SDK", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["embedded", "exploited", "infrastructure", "realtek", "routers", "self-hosted"]
not_affected_if: ["no-realtek-sdk-firmware", "web-admin-interface-disabled"]
published_at: "2021-08-16T12:15:07+00:00"
first_seen_at: "2026-10-23T19:11:53+00:00"
updated_at: "2026-10-23T21:57:34+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-35395", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-35395", "first_seen_at": "2026-10-23T19:13:43+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-35395", "first_seen_at": "2026-10-23T21:57:34+00:00"}]
---

# Realtek AP-Router SDK: Realtek AP-Router SDK Buffer Overflow Vulnerability

Realtek AP-Router SDK firmware's boa HTTP web server has a buffer overflow from unsafe copies of overly long form parameters. The source says it leads to denial of service; CISA lists it as actively exploited, so attackers are likely using it against routers that run this SDK.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Realtek AP-Router SDK affected ? fixed ?

## Fix

Apply the vendor firmware update per Realtek or the router vendor's instructions (CISA required action). Specific fixed version: unknown

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-35395
- 2026-10-23T19:13:43+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-35395
- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-35395

## From the sources

Realtek Jungle SDK version v2.x up to v3.4.14B provides an HTTP web server exposing a management interface that can be used to configure the access point. Two versions of this management interface exists: one based on Go-Ahead named webs and another based on Boa named boa. Both of them are affected by these vulnerabilities. Specifically, these binaries are vulnerable to the following issues: - stack buffer overflow in formRebootCheck due to unsafe copy of submit-url parameter - stack buffer overflow in formWsc due to unsafe copy of submit-url parameter - stack buffer overflow in formWlanMultipleAP due to unsafe copy of submit-url parameter - stack buffer overflow in formWlSiteSurvey due to unsafe copy of ifname parameter - stack buffer overflow in formStaticDHCP due to unsafe copy of hostname parameter - stack buffer overflow in formWsc due to unsafe copy of 'peerPin' parameter - arbitrary command execution in formSysCmd via the sysCmd parameter - arbitrary command injection in formWsc via the 'peerPin' parameter Exploitability of identified issues will differ based on what the end vendor/manufacturer did with the Realtek SDK webserver. Some vendors use it as-is, others add their own authentication implementation, some kept all the features from the server, some remove some of them, some inserted their own set of features. However, given that Realtek SDK implementation is full of insecure calls and that developers tends to re-use those examples in their custom code, any binary based on Realtek SDK webserver will probably contains its own set of issues on top of the Realtek ones (if kept). Successful exploitation of these issues allows remote attackers to gain arbitrary code execution on the device.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_