Home > Articles > Programming > Windows Programming

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

2.6 Code Injection

When the return address is overwritten as the result of a software flaw, it seldom points to valid instructions. Consequently, transferring control to this address typically causes an exception and results in a corrupted stack. However, it is possible for an attacker to create a specially crafted string that contains a pointer to some malicious code, which the attacker also provides. When the subroutine returns, control is then transferred to this code. The malicious code runs with the permissions that the vulnerable program has when the subroutine returns. This is why programs running with root or other elevated privileges are normally targeted. The malicious code can perform any function that can otherwise be programmed, but often will simply open a remote shell on the compromised machine. For this reason the injected, malicious code is referred to as shellcode.

The pièce de résistance of any good exploit is the malicious argument. A malicious argument must have several characteristics.

  • It must be accepted by the vulnerable program as legitimate input.
  • The argument, along with other controllable inputs, must result in execution of the vulnerable code path.
  • The argument must not cause the program to terminate abnormally before control is passed to the shellcode.

The get password program shown in Figure 2–9 can also be exploited to execute arbitrary code. This time, the program was compiled for Red Hat Linux 9.0 using GCC. An exploit can be injected into the program via a binary data file (as shown in Figure 2–24) from a file using redirection as follows:

%" "./BufferOverflow < exploit.bin 

The binary data file cannot contain any newline or null characters until the last byte because the exploit relies on the string function gets(). The gets() function interprets a null character as a string termination character and reads data until a newline character or EOF condition is encountered.

000 31 32 33 34 35 36 37 38-39 30 31 32 33 34 35 36 "1234567890123456" 
010 37 38 39 30 31 32 33 34-35 36 37 38 E0 F9 FF BF "789012345678a· +" 
020 31 C0 A3 FF F9 FF BF B0-0B BB 03 FA FF BF B9 FB "1+ú · +≠+· +≠v" 
030 F9 FF BF 8B 15 FF F9 FF-BF CD 80 FF F9 FF BF 31 "· +ï§ · +-Ç · +1" 
040 31 31 31 2F 75 73 72 2F-62 69 6E 2F 63 61 6C 0A "111/usr/bin/cal " 

Figure 2–24. Contents of binary file exploit.bin containing shellcode

Figure 25

Figure 2–25. Program stack overwritten by binary exploit

When the exploit code is injected into the get password program, the program stack is overwritten as shown in Figure 2–25, and the exploit works as follows.

  1. The first 16 bytes of binary data (line 1) fill the allocated storage space for the password. Even though the program only allocated 12 bytes for the password, the version of the gcc compiler that was used to compile the program allocates stack data in multiples of 16 bytes.
  2. The next 12 bytes of binary data (line 2) fill the extra storage space that was created by the compiler to keep the stack aligned on a 16-byte boundary. Only 12 bytes are allocated by the compiler because the stack already contained a 4-byte return address when the function was called.
  3. The return address has been overwritten (line 3) to resume program execution (line 4) when the program executes the return in the function IsPasswordOkay(). This results in the execution of code contained on the stack (lines 4–10).
  4. Create a zero value and use it to NULL terminate the argument list (lines 4 and 5). This is necessary because an argument to a system call made by this exploit must contain a list of character pointers terminated by a NULL pointer. Because the exploit cannot contain null characters until the last byte, the NULL pointer must be set by the exploit code.
  5. The system call is set to 0xb, which equates to the execve() system call in Linux (line 6).
  6. The three arguments for the execve() function call are set up (lines 7–9). The data for these arguments is located in lines 12–13.
  7. The execve() system call is executed, which results in the execution of the Linux calender program (line 10), as shown in Figure 2–26.

Reverse engineering of the code can be used to determine the exact offset from the buffer to the return address in the stack frame, which leads to the location of the injected shellcode. However, it is possible to soften these requirements [Aleph One 96]. For example, the location of the return address can be approximated by repeating the return address several times in the approximate region of the return address. Assuming a 32-bit architecture, the return address is normally 4-byte aligned. Even if the return address is offset, there are only 4

Figure 26

Figure 2–26. Execution result of the code injection exploit

possibilities to test. The location of the shellcode can also be approximated by prefacing the shellcode with nop instructions.7 The exploit need only jump somewhere in the field of nop instructions to execute the shellcode.

Most real-world stack smashing attacks behave in this fashion; that is, overwriting the return address to transfer control to injected code. Exploits that simply change the return address to jump to a new location in the code are less common, partly because these vulnerabilities are harder to find (it depends on finding program logic that can be bypassed) and less useful to an attacker (only allowing access to one program as opposed to running arbitrary code).

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020