Realtek Jungle SDK Remote Code Execution and Command Injection Vulnerability (CVE-2021-35395) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTIoT and network devices utilizing Realtek Jungle SDK versions v2.x through v3.4.14B
Unauthenticated remote attackers can exploit stack buffer overflows and command injection flaws to execute arbitrary code with root privileges, leading to full device compromise
Apply the latest firmware updates from the respective device manufacturers and restrict external access to the web management interface
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Users must apply the latest firmware updates provided by their respective device vendors. For developers and system integrators, upgrade the Realtek SDK to version v3.4.14C or higher to ensure the vulnerable binaries are replaced.
2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, block external access to the web administration ports (e.g., 80, 443, 8080) using firewall rules. Below is an example of restricting access using iptables:
# Block external HTTP/HTTPS access to the management interface on WAN interface (e.g., eth0)
iptables -A INPUT -i eth0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i eth0 -p tcp --dport 443 -j DROP
iptables -A INPUT -i eth0 -p tcp --dport 8080 -j DROP
# Allow access only from a trusted management subnet
iptables -A INPUT -p tcp -s 192.168.1.0/24 --dport 80 -j ACCEPT3. Log Audit & IoC Verification Commands
Inspect web server access logs and network traffic for suspicious requests containing parameters associated with the exploit payloads.
# Search web server logs for exploit attempts targeting known vulnerable parameters
grep -Ei 'sysCmd|peerPin|submit-url' /var/log/nginx/access.log /var/log/httpd/access.log 2>/dev/null
# Monitor live network traffic for potential exploitation attempts using tcpdump
tcpdump -nn -A -i eth0 'tcp port 80 and (tcp[((tcp & 0xf0) >> 2):4] = 0x504f5354)' | grep -Ei 'sysCmd|peerPin'Stop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability exists within the web server components ('webs' based on Go-Ahead and 'boa' based on Boa) provided by the Realtek Jungle SDK. The root cause is the unsafe handling of user-supplied input parameters within the web management interface. Specifically, functions such as formRebootCheck, formWsc, formWlanMultipleAP, formWlSiteSurvey, and formStaticDHCP perform unsafe copy operations of parameters like submit-url, peerPin, and hostname into stack buffers without proper boundary validation, leading to stack-based buffer overflows. Additionally, the formSysCmd interface fails to sanitize the sysCmd parameter, resulting in arbitrary command injection.
2. Exploitation Mechanics & Attack Scenario
An attacker can exploit these vulnerabilities by sending crafted HTTP POST requests to the vulnerable web server endpoints. For command injection, the attacker injects shell metacharacters (e.g., ;, &, |) along with malicious payloads into the sysCmd or peerPin parameters, which are then executed directly by the system shell. For the stack buffer overflow, sending an excessively long string in the submit-url parameter overwrites the stack's return address, allowing the attacker to hijack the execution flow and execute arbitrary shellcode with administrative privileges.
3. Infrastructure & Business Impact
As this vulnerability is actively exploited in the wild and listed in the CISA KEV catalog, it poses a severe threat to enterprise and consumer networks. Successful exploitation allows threat actors to recruit compromised devices into DDoS botnets, establish persistent backdoors, perform lateral movement within the internal network, and intercept sensitive network traffic, causing significant operational disruption and data exposure.
Official Vendor Advisories & References
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.
Frequently Asked SecOps Questions (CVE-2021-35395)
FAQQ1. How critical is CVE-2021-35395 and is it actively exploited in the wild?
CVE-2021-35395 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 98.1%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-35395?
Primary impacted vendors include realtek across jungle_sdk. Scope summary: All OEM/ODM network devices (routers, access points, IP cameras) integrated with Realtek Jungle SDK v2.x through v3.4.14B
Q3. What temporary mitigations or workarounds exist for CVE-2021-35395 before patching?
[Mitigation] Apply the latest firmware updates from the respective device manufacturers and restrict external access to the web management interface Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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