Recently it was discovered as a part of the research on IoT devices in the most recent firmware for Shekar Endoscope that the desktop application used to connect to the device suffers from a stack overflow if more than 26 characters are passed to it as the Wi-Fi password. This application is installed on the device and an attacker who can provide the right payload can execute code on the users system directly. Any breach of this system can allow an attacker to get access to all the data that the user has access too. The application uses a dynamic link library(DLL) called avilib.dll which is used by the application to send binary packets to the device that allow to control the device. One such action that the DLL provides is change password in the function sendchangepass which allows a user to change the Wi-Fi password on the device. This function calls a sub function sub_75876EA0 at address 0x7587857C. The function determines which action to execute based on the parameters sent to it. The sendchangepass passes the datastring as the second argument which is the password we enter in the textbox and integer 2 as first argument. The rest of the 3 arguments are set to 0. The function sub_75876EA0 at address 0x75876F19 uses the first argument received and to determine which block to jump to. Since the argument passed is 2, it jumps to 0x7587718C and proceeds from there to address 0x758771C2 which calculates the length of the data string passed as the first parameter.This length and the first argument are then passed to the address 0x7587726F which calls a memmove function which uses a stack address as the destination where the password typed by us is passed as the source and length calculated above is passed as the number of bytes to copy which leads to a stack overflow.
The product performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Endoscope_camera_firmware | Ishekar | * | * |
Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced. This can cause read or write operations to be performed on memory locations that may be associated with other variables, data structures, or internal program data. As a result, an attacker may be able to execute arbitrary code, alter the intended control flow, read sensitive information, or cause the system to crash.
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.
Be wary that a language’s interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.
D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
Consider adhering to the following rules when allocating and managing an application’s memory:
Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.
Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.
For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.
For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].