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Upgrade to ProDetect DD-WRT Stack-Based Buffer Overflow Exploitation Attempt (CVE-2021-27137) in Sumo Logic CSE
Detects exploitation attempts against a stack-based buffer overflow vulnerability (CWE-121) in DD-WRT firmware. The flaw allows an attacker with network access to the DD-WRT web management interface to trigger a stack overflow via crafted HTTP requests, potentially leading to remote code execution or denial of service on the router/embedded device. This CVE is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. Detection focuses on abnormal HTTP requests to DD-WRT management interfaces (oversized parameters, malformed CGI requests), unexpected crash/restart of httpd or DD-WRT management processes, and post-exploitation network behavior originating from embedded/IoT network segments.
MITRE ATT&CK
- Tactic
- Initial Access Impact Execution
Sumo Detection Query
_sourceCategory=network/firewall OR _sourceCategory=web/proxy
| where dest_port matches "80" or dest_port matches "443" or dest_port matches "8080"
| where uri matches "*cgi-bin*" or uri matches "*apply.cgi*" or uri matches "*management.asp*"
| parse regex field=uri "(?<uri_len>.{2000,})" nodrop
| if (isNull(uri_len) and !(uri matches "*%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25*"), "benign", "suspicious") as verdict
| where verdict = "suspicious"
| count by src_ip, dest_ip, uri
| where _count >= 3Sumo Logic search identifying suspiciously long or percent-encoded requests to DD-WRT CGI management paths that may indicate stack overflow exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate long-form configuration URLs from admin tools
- Vulnerability scanning conducted under change control
- Encoded characters from internationalized device names or SSIDs
Other platforms for CVE-2021-27137
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Oversized CGI Parameter Request
Expected signal: Firewall/proxy log entry showing a GET request to /apply.cgi with a URI length exceeding 2000 characters from the test source IP.
- Test 2Hex-Encoded Payload Simulation
Expected signal: Web/proxy log capturing a request URI containing repeated %41-style percent-encoded sequences exceeding 100 occurrences.
- Test 3Repeated Burst Requests to Management Interface
Expected signal: Four distinct oversized HTTP requests to /cgi-bin/config.exe logged from the same source IP within a 5-minute window.
References (4)
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