Executive brief
The D-Link DWR-932B LTE router uses a predictable method for generating Wi-Fi Protected Setup (WPS) PINs. Because the security codes are generated using the current system time as a starting point, an attacker can easily calculate the valid PIN. This allows an unauthorized person within range of the Wi-Fi signal to bypass wireless security and join the network.
Technical details
The D-Link DWR-932B (Revision B) router suffers from a weak pseudo-random number generator (PRNG) implementation in its WPS PIN generation logic. The firmware seeds the PRNG using 'srand(time(0))', where 'time(0)' represents the current Unix epoch time. Since the router synchronizes its clock via NTP, the seed value is highly predictable. An attacker can reverse-engineer the PIN generation algorithm and, by estimating the router's system time, generate a small set of potential WPS PINs. This significantly reduces the entropy of the 8-digit PIN, allowing for trivial brute-force attacks to gain unauthorized access to the wireless network. At the time of disclosure, no official patches were available for this legacy device.
Affected products
- D-Link DWR-932B firmware revB 2.02.EU and earlier
- D-Link DWR-932B Revision B
Timeline
- 2016-09-28: disclosed: Initial public disclosure by researcher Pierre Kim
- 2017-01-30: advisory: NVD publication date