Atomicorp WAF Research Note: CVE-2021-35395

RealTek Jungle SDK - Arbitrary Command Injection

CVE Details

• Already protected by existing Atomicorp WAF rules
• Protection status: Understanding Atomicorp WAF Protection Status
• CVE: CVE-2021-35395
• Name: RealTek Jungle SDK - Arbitrary Command Injection
• Severity: Critical
• CVSS: 9.8 (v3.1) (Critical)
• CVSS version: 3.1
• CVSS source: NVD
• CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • Attack vector: Network
  • Attack complexity: Low
  • Privileges required: None
  • User interaction: None
  • Scope: Unchanged
  • Confidentiality impact: High
  • Integrity impact: High
  • Availability impact: High
• CWE: N/A
• Vendor: realtek
• Vulnerable products: rtl819x jungle software development kit , realtek jungle sdk
• CVE published: 2021-08-16
• CVE last modified: 2026-06-17
• Affected versions (NVD configurations):
  • rtl819x jungle software development kit: >= 2.0, <= 3.4.14b
• EPSS: 0.9796; 99.9th percentile (FIRST (opens in a new tab) )
• CISA KEV: Listed (added 2021-11-03)
  • Known ransomware campaign use: Unknown
• Latest Update: 2026-09-06
• Selected Rule IDs observed: 340014 , 340029 , 344361 , 344363
• Matching rules: 4; rules with blocking actions: 4
• Would-block Rule IDs: 340014 , 340029 , 344361 , 344363
• Request surfaces inspected: JSON request data, Request URI, Request argument names, Request arguments, Request cookies, SOAP request data, XML request data

Vulnerability Description

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.

Recommended Actions

1. Maintain the observed Atomicorp protections. Keep your Atomicorp commercial rules current and confirm that the selected observed rules (340014 , 340029 , 344361 , 344363 ) have not been locally disabled. Atomicorp commercial rules are enabled by default. If you use Atomic WAF, review the applicable policy and rule settings.

2. Apply the vendor’s remediation. WAF protection is defense in depth and does not replace upgrading or following the affected vendor’s guidance.

   • The CVE record does not include written upgrade or workaround instructions, but it does publish the following patch or mitigation reference:
     • Patch or mitigation information (opens in a new tab)
     • Patch or mitigation information (opens in a new tab)
   • CISA KEV required action: Apply updates per vendor instructions.
   • CISA KEV federal remediation due date: 2021-11-17

3. Validate after changes. Confirm rule updates are current, review WAF events for the affected application, and test application behavior after vendor upgrades, mitigations, or local policy changes.

Research Notes

Atomicorp WAF protections are designed around attack techniques and exploit behaviors, allowing existing protections to apply across multiple vulnerabilities without requiring a unique rule for every CVE.

Public Vulnerability References

• NVD (opens in a new tab)
• CVE Record (opens in a new tab)
• Exploit or technical research: https://www.iot-inspector.com/blog/advisory-multiple-issues-realtek-sdk-iot-supply-chain (opens in a new tab)
• Vendor advisory: https://www.realtek.com/en/cu-1-en/cu-1-taiwan-en (opens in a new tab)
• Patch or mitigation: https://www.realtek.com/images/safe-report/Realtek_APRouter_SDK_Advisory-CVE-2021-35392_35395.pdf (opens in a new tab)
• CVE authority reference: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-35395 (opens in a new tab)

Test or Research Source

• Source: http/cves/2021/CVE-2021-35395.yaml (opens in a new tab)
• Tags: cve, cve2021, kev, rce, realtek, vkev, vuln

Research Note Context

This research note documents exploit-technique analysis associated with this vulnerability and references Atomicorp WAF protections observed during engineering review, testing, or validation activities.

Atomicorp security controls are generally designed to identify and mitigate attack techniques and exploit behaviors rather than individual CVE identifiers. As a result, protections developed for one vulnerability may also apply to related attack variants and future vulnerabilities using similar techniques.

Learn More

Atomicorp develops commercially supported security technologies for web applications, servers, endpoints, workloads, and legacy enterprise platforms.

Organizations interested in protecting systems against exploit techniques associated with vulnerabilities such as this one can learn more about:

• Atomic ModSecurity Rules: commercially maintained WAF rules for ModSecurity deployments, including protections for web attacks, bots, scanners, malware, exploitation attempts, and emerging vulnerability classes.
• Atomic WAF: an enterprise web application firewall with Atomicorp rules, centralized management, reporting, authentication controls, and operational tooling.
• Atomic ModSecurity Integrator: a special licensing option for MSPs, MSSPs, OEMs, VARs, reverse proxy providers, and other integrators who want to incorporate Atomicorp ModSecurity rule technology into their own products or services.
• Atomic OSSEC: an enterprise OSSEC-based intrusion detection, compliance, and security monitoring platform.
• Atomic Protector: workload protection for Linux, web, cloud, data center, and hybrid environments.

For additional information, product evaluations, or technical discussions, visit https://www.atomicorp.com/ or https://modsecurity.io/ (opens in a new tab) .