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Mir Khan

Interators are usually implemented using signed integers like the typical "for (int i=0; ..." and in fact is the type used indexing "cstr[i]", most of methods use the signed int, int by default is signed.
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:29
29 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:

See below the command "i r rax" to view the address where the write will be performed.

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()

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Mir Khan

Welcome to my 4th new tutorial of the series of networking. In this blog you'll the content about network switches. You'll learn about how to make a communication successful and secure in the same network (LAN) by using STP. As Spanning tree protocol (STP) we used in multi-switched networks. Why we use this protocol in multi-switched network etc.

What is Switch?

A switch is an intelligent device used to connect multiple devices within the same network. The intelligence of is that it requires Media Access Control (MAC) address for communication and doesn't allow broadcast. Let's understand the whole thing by a little example, consider there is a network having 3 end devices name Device-A, Device-B,Device-C connected with each other respectively with the help of switch. When a Device-A sends data to Device-C so that data will only forwarded by switch to Device-C not to Device-B.

What is Media Access Control (MAC) address?

A Media Access Control (MAC) address is 48-bit unique physical address given to network interface controller (NIC) or network adapter, for communication within the same network which is given by its manufacturer. It is made up of hexadecimal numbers like a1:b1:cc:ac:2e:f1.

What is STP?

STP stands for Spanning tree protocol which is basically used in bridge and switches to prevent loops when you have a redundant links in the Ethernet networks. If the loop is present in the Ethernet network so the whole network will suffer because there will MAC instability in the MAC table, duplicate frames generation and so on. Let's move to the video for further detail.

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Mir Khan

Social engineering is a nontechnical method of breaking into a system or network. It's the process of deceiving users of a system and convincing them to perform acts useful to the hacker, such as giving out information that can be used to defeat or bypass security mechanisms. Social engineering is important to understand because hackers can use it to attack the human element of a system and circumvent technical security measures. This method can be used to gather information before or during an attack.

A social engineer commonly uses the telephone or Internet to trick people into revealing sensitive information or to get them to do something that is against the security policies of the organization. By this method, social engineers exploit the natural tendency of a person to trust their word, rather than exploiting computer security holes. It's generally agreed that users are the weak link in security; this principle is what makes social engineering possible.

The most dangerous part of social engineering is that companies with authentication processes, firewalls, virtual private networks, and network monitoring software are still wide open to attacks, because social engineering doesn't assault the security measures directly. Instead, a social-engineering attack bypasses the security measures and goes after the human element in an organization.

Types of Social Engineering-Attacks

There are two types of Social Engineering attacks

Human-Based

Human-based social engineering refers to person-to-person interaction to retrieve the desired information. An example is calling the help desk and trying to find out a password.

Computer-Based

Computer-based social engineering refers to having computer software that attempts to retrieve the desired information. An example is sending a user an email and asking them to reenter a password in a web page to confirm it. This social-engineering attack is also known as phishing.

Human-Based Social Engineering

Human-Based further categorized as follow:

Impersonating an Employee or Valid User

In this type of social-engineering attack, the hacker pretends to be an employee or valid user on the system. A hacker can gain physical access by pretending to be a janitor, employee, or contractor. Once inside the facility, the hacker gathers information from trashcans, desktops, or computer systems.

Posing as an Important User

In this type of attack, the hacker pretends to be an important user such as an executive or high-level manager who needs immediate assistance to gain access to a computer system or files. The hacker uses intimidation so that a lower-level employee such as a help desk worker will assist them in gaining access to the system. Most low-level employees won't question someone who appears to be in a position of authority.

Using a Third Person

Using the third-person approach, a hacker pretends to have permission from an authorized source to use a system. This attack is especially effective if the supposed authorized source is on vacation or can't be contacted for verification.

Calling Technical Support

Calling tech support for assistance is a classic social-engineering technique. Help desk and technical support personnel are trained to help users, which makes them good prey for social-engineering attacks.

Shoulder Surfing

Shoulder surfing is a technique of gathering passwords by watching over a person's shoulder while they log in to the system. A hacker can watch a valid user log in and then use that password to gain access to the system.

Dumpster Diving

Dumpster diving involves looking in the trash for information written on pieces of paper or computer printouts. The hacker can often find passwords, filenames, or other pieces of confidential information.

Computer-Based Social Engineering

Computer-based social-engineering attacks can include the following:

Email attachments
Fake websites
Pop-up windows

Insider Attacks

If a hacker can't find any other way to hack an organization, the next best option is to infiltrate the organization by getting hired as an employee or finding a disgruntled employee to assist in the attack. Insider attacks can be powerful because employees have physical access and are able to move freely about the organization. An example might be someone posing as a delivery person by wearing a uniform and gaining access to a delivery room or loading dock. Another possibility is someone posing as a member of the cleaning crew who has access to the inside of the building and is usually able to move about the offices. As a last resort, a hacker might bribe or otherwise coerce an employee to participate in the attack by providing information such as passwords.

Identity Theft

A hacker can pose as an employee or steal the employee's identity to perpetrate an attack. Information gathered in dumpster diving or shoulder surfing in combination with creating fake ID badges can gain the hacker entry into an organization. Creating a persona that can enter the building unchallenged is the goal of identity theft.

Phishing Attacks

Phishing involves sending an email, usually posing as a bank, credit card company, or other financial organization. The email requests that the recipient confirm banking information or reset passwords or PINs. The user clicks the link in the email and is redirected to a fake website. The hacker is then able to capture this information and use it for financial gain or to perpetrate other attacks. Emails that claim the senders have a great amount of money but need your help getting it out of the country are examples of phishing attacks. These attacks prey on the common person and are aimed at getting them to provide bank account access codes or other confidential information to the hacker.

Online Scams

Some websites that make free offers or other special deals can lure a victim to enter a username and password that may be the same as those they use to access their work system.
The hacker can use this valid username and password once the user enters the information in the website form. Mail attachments can be used to send malicious code to a victim's system, which could automatically execute something like a software keylogger to capture passwords. Viruses, Trojans, and worms can be included in cleverly crafted emails to entice a victim to open the attachment. Mail attachments are considered a computer-based social-engineering attack.More articles

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Wednesday, May 31, 2023

C++ Std::String Buffer Overflow And Integer Overflow

Networking | Routing And Switching | Tutorial 4 | 2018