Nevertheless, the "std::string::operator[]" index is size_t which is unsigned, and so does size(), and same happens with vectors.
Besides the operator[] lack of negative index control, I will explain this later.
Do the compilers doesn't warn about this?
If his code got a large input it would index a negative numer, let see g++ and clang++ warnings:
No warnings so many bugs out there...
In order to reproduce the crash we can load a big string or vector from file, for example:
I've implemented a loading function, getting the file size with tellg() and malloc to allocate the buffer, then in this case used as a string.
Let see how the compiler write asm code based on this c++ code.
So the string constructor, getting size and adding -2 is clear. Then come the operator<< to concat the strings.
Then we see the operator[] when it will crash with the negative index.
In assembly is more clear, it will call operator[] to get the value, and there will hapen the magic dereference happens. The operator[] will end up returning an invalid address that will crash at [RAX]
In gdb the operator[] is a allq 0x555555555180 <_znst7__cxx1112basic_stringicst11char_traitsicesaiceeixem plt="">
(gdb) i r rsi
rsi 0xfffffffffffefffe -65538
The implmementation of operator ins in those functions below:
(gdb) bt
#0 0x00007ffff7feebf3 in strcmp () from /lib64/ld-linux-x86-64.so.2
#1 0x00007ffff7fdc9a5 in check_match () from /lib64/ld-linux-x86-64.so.2
#2 0x00007ffff7fdce7b in do_lookup_x () from /lib64/ld-linux-x86-64.so.2
#3 0x00007ffff7fdd739 in _dl_lookup_symbol_x () from /lib64/ld-linux-x86-64.so.2
#4 0x00007ffff7fe1eb7 in _dl_fixup () from /lib64/ld-linux-x86-64.so.2
#5 0x00007ffff7fe88ee in _dl_runtime_resolve_xsavec () from /lib64/ld-linux-x86-64.so.2
#6 0x00005555555554b3 in main (argc=2, argv=0x7fffffffe118) at main.cpp:29
Then crashes on the MOVZX EAX, byte ptr [RAX]
Program received signal SIGSEGV, Segmentation fault.
0x00005555555554b3 in main (argc=2, argv=0x7fffffffe118) at main.cpp:2929 cout << "penultimate byte is " << hex << s[i] << endl;
(gdb)
What about negative indexing in std::string::operator[] ?
It's exploitable!
In a C char array is known that having control of the index, we can address memory.
Let's see what happens with C++ strings:
The operator[] function call returns the address of string plus 10, and yes, we can do abitrary writes.
Note that gdb displays by default with at&t asm format wich the operands are in oposite order:
And having a string that is in the stack, controlling the index we can perform a write on the stack.
To make sure we are writing outside the string, I'm gonna do 3 writes:
The beginning of the std::string object is 0x7fffffffde50.
Write -10 writes before the string 0x7fffffffde46.
And write -100 segfaults because is writting in non paged address.
So, C++ std::string probably is not vulnerable to buffer overflow based in concatenation, but the std::string::operator[] lack of negative indexing control and this could create vulnerable and exploitable situations, some times caused by a signed used of the unsigned std::string.size()
Related news
- What Are Hacking Tools
- Pentest Tools
- Pentest Tools Free
- Hacker Tools For Pc
- Hacker Tools Software
- Hacking Tools Kit
- Hacker Tool Kit
- Hacker Tools Mac
- Pentest Tools Online
- Hack App
- Pentest Tools Linux
- Hack Website Online Tool
- Pentest Tools Open Source
- Pentest Tools Port Scanner
- Black Hat Hacker Tools
- Best Pentesting Tools 2018
- Pentest Tools Url Fuzzer
- Hacker Tools For Windows
- Hacking App
- How To Hack
- Best Hacking Tools 2019
- Pentest Tools
- Pentest Tools Subdomain
- Tools Used For Hacking
- Hack Tool Apk
- Nsa Hack Tools Download
- Hacking Tools
- Hack Tools Mac
- Hack Tools For Ubuntu
- Easy Hack Tools
- Hacker Tools Linux
- Hacking Tools 2019
- Hacker Techniques Tools And Incident Handling
- Wifi Hacker Tools For Windows
- Github Hacking Tools
- Hacking Tools For Windows Free Download
- Hacker Tools Windows
- Pentest Tools Port Scanner
- Hacker Tools For Ios
- Pentest Tools Linux
- New Hack Tools
- Hack Tools Mac
- Easy Hack Tools
- Hacking Tools Online
- Hacker Tools Mac
- Hack Tools
- Hacker Tool Kit
- Pentest Tools Bluekeep
- Hacker Tool Kit
- Install Pentest Tools Ubuntu
- World No 1 Hacker Software
- Pentest Tools Android
- World No 1 Hacker Software
- Hacking Tools For Kali Linux
- Hacking Tools Free Download
- Pentest Tools Download
- Game Hacking
- How To Make Hacking Tools
- Growth Hacker Tools
- Hacker Tools List
- Hacking Tools Github
- Pentest Tools Port Scanner
- Pentest Tools Website
- Hacker Tools
- How To Make Hacking Tools
- Hacker Tools Github
- Hacker Tools
- Hacker Tools Free Download
- Pentest Tools Find Subdomains
- Pentest Tools Apk
- Physical Pentest Tools
- Best Pentesting Tools 2018
- Hacking Tools 2020
- Hacker Tools Free
- Hack Tools For Pc
- New Hack Tools
- Hacking Tools Github
- Ethical Hacker Tools
- Pentest Tools For Ubuntu
- How To Make Hacking Tools
- Hack Tool Apk
- Hack Tools Github
- Hack Tools Mac
- Pentest Tools For Mac
- Hacking Tools And Software
- Hack Tools
- Top Pentest Tools
- Hacking Tools Usb
- Hacker Security Tools
- Black Hat Hacker Tools
- Hacker Tools
