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How the CVE Works: This vulnerability exists in the `cgibin` binary’s `hnap_main()` function on affected D-Link routers. The function uses `sprintf()` unsafely to copy user-controlled data from the HTTP request’s `SERVER_NAME` environment variable into a fixed-size stack buffer without proper bounds checking. An attacker can send a specially crafted HTTP request with an excessively long hostname in the `Host:` header. This overflows the buffer, corrupting adjacent stack memory, including the return address. By precisely crafting the overflow data, an attacker can hijack the program’s execution flow to run their own malicious shellcode, ultimately leading to remote code execution with root privileges on the device.
DailyCVE Form:
Platform: D-Link Routers
Version: revA v101b03
Vulnerability: Buffer Overflow
Severity: Critical
Date: 2021-03-05
Prediction: 2021-06-30
What Undercode Say:
Analytics:
strings ./cgibin | grep -A5 -B5 hnap_main objdump -d ./cgibin | grep -A20 "<hnap_main>:" curl -H "Host: $(python -c 'print "A"800')" http://<router_ip>/hnap_main
How Exploit:
Craft HTTP request with long Host header targeting `/hnap_main` endpoint to trigger stack overflow and overwrite return address, gaining shell.
Protection from this CVE:
Apply firmware update. Disable WAN management. Use network segmentation.
Impact:
Remote Code Execution. Full Device Compromise. Unauthorized Root Access.
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Sources:
Reported By: www.cve.org
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