CWE-834: Excessive Iteration

Description

The product performs an iteration or loop without sufficiently limiting the number of times that the loop is executed.

If the iteration can be influenced by an attacker, this weakness could allow attackers to consume excessive resources such as CPU or memory. In many cases, a loop does not need to be infinite in order to cause enough resource consumption to adversely affect the product or its host system; it depends on the amount of resources consumed per iteration.

Potential Impact

Availability

DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory), DoS: Amplification, DoS: Crash, Exit, or Restart

Demonstrative Examples

In this example a mistake exists in the code where the exit condition contained in flg is never called. This results in the function calling itself over and over again until the stack is exhausted.

Bad

void do_something_recursive (int flg)
	       {
	       
		 ... // Do some real work here, but the value of flg is unmodified
		 if (flg) { do_something_recursive (flg); }    // flg is never modified so it is always TRUE - this call will continue until the stack explodes
	       
	       }
	       int flag = 1; // Set to TRUE
	       do_something_recursive (flag);

Note that the only difference between the Good and Bad examples is that the recursion flag will change value and cause the recursive call to return.

Good

void do_something_recursive (int flg)
	       {
	       
		 ... // Do some real work here
		 // Modify value of flg on done condition
		 if (flg) { do_something_recursive (flg); }    // returns when flg changes to 0
	       
	       }
	       int flag = 1; // Set to TRUE
	       do_something_recursive (flag);

For this example, the method isReorderNeeded is part of a bookstore application that determines if a particular book needs to be reordered based on the current inventory count and the rate at which the book is being sold.

Bad

public boolean isReorderNeeded(String bookISBN, int rateSold) {
               
                 boolean isReorder = false;
                 int minimumCount = 10;int days = 0;
                 
                 // get inventory count for book
                 int inventoryCount = inventory.getIventoryCount(bookISBN);
                 
                 // find number of days until inventory count reaches minimum
                 while (inventoryCount > minimumCount) {
                 
                   inventoryCount = inventoryCount - rateSold;days++;
                 
                 }
                 
                 // if number of days within reorder timeframe
                 
                 
                 // set reorder return boolean to true
                 if (days > 0 && days < 5) {isReorder = true;}
               return isReorder;
               }

However, the while loop will become an infinite loop if the rateSold input parameter has a value of zero since the inventoryCount will never fall below the minimumCount. In this case the input parameter should be validated to ensure that a value of zero does not cause an infinite loop, as in the following code.

Good

public boolean isReorderNeeded(String bookISBN, int rateSold) {
               ...
               
               // validate rateSold variable
               if (rateSold < 1) {return isReorder;}
               ...
               }

Detection Methods

Dynamic Analysis with Manual Results Interpretation SOAR Partial — According to SOAR [REF-1479], the following detection techniques may be useful:
Manual Static Analysis - Source Code SOAR Partial — According to SOAR [REF-1479], the following detection techniques may be useful:
Automated Static Analysis - Source Code High — According to SOAR [REF-1479], the following detection techniques may be useful:
Architecture or Design Review High — According to SOAR [REF-1479], the following detection techniques may be useful:

Real-World CVE Examples

CVE ID	Description
CVE-2011-1027	Chain: off-by-one error (CWE-193) leads to infinite loop (CWE-835) using invalid hex-encoded characters.
CVE-2006-6499	Chain: web browser crashes due to infinite loop - "bad looping logic [that relies on] floating point math [CWE-1339] to exit the loop [CWE-835]"

Frequently Asked Questions

What is CWE-834?

CWE-834 (Excessive Iteration) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Class-level weakness. The product performs an iteration or loop without sufficiently limiting the number of times that the loop is executed.

How can CWE-834 be exploited?

Attackers can exploit CWE-834 (Excessive Iteration) to dos: resource consumption (cpu), dos: resource consumption (memory), dos: amplification, dos: crash, exit, or restart. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-834?

Follow secure coding practices, conduct code reviews, and use automated security testing tools (SAST/DAST) to detect this weakness early in the development lifecycle.

What is the severity of CWE-834?

CWE-834 is classified as a Class-level weakness (High abstraction). It has been observed in 2 real-world CVEs.