CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')
Weakness ID: 835
Abstraction: Base Structure: Simple
Status: Incomplete
Presentation Filter:
Description
The program contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.
Extended Description
If the loop can be influenced by an attacker, this weakness could allow attackers to consume excessive resources such as CPU or memory.
Relationships
The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
Relevant to the view "Research Concepts" (CWE-1000)
Nature
Type
ID
Name
ChildOf
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
Base - a weakness
that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
Nature
Type
ID
Name
ChildOf
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.
The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
An infinite loop will cause unexpected consumption of resources, such as CPU cycles or memory. The software's operation may slow down, or cause a long time to respond.
Demonstrative Examples
Example 1
In the following code the method processMessagesFromServer attempts to establish a connection to a server and read and process messages from the server. The method uses a do/while loop to continue trying to establish the connection to the server when an attempt fails.
(bad code)
Example Language: C
int processMessagesFromServer(char *hostaddr, int port) {
... int servsock; int connected; struct sockaddr_in servaddr;
// create socket to connect to server servsock = socket( AF_INET, SOCK_STREAM, 0); memset( &servaddr, 0, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_port = htons(port); servaddr.sin_addr.s_addr = inet_addr(hostaddr);
do {
// establish connection to server connected = connect(servsock, (struct sockaddr *)&servaddr, sizeof(servaddr));
// if connected then read and process messages from server if (connected > -1) {
// read and process messages ...
}
// keep trying to establish connection to the server } while (connected < 0);
// close socket and return success or failure ...
}
However, this will create an infinite loop if the server does not respond. This infinite loop will consume system resources and can be used to create a denial of service attack. To resolve this a counter should be used to limit the number of attempts to establish a connection to the server, as in the following code.
(good code)
Example Language: C
int processMessagesFromServer(char *hostaddr, int port) {
... // initialize number of attempts counter int count = 0; do {
// establish connection to server connected = connect(servsock, (struct sockaddr *)&servaddr, sizeof(servaddr));
// increment counter count++;
// if connected then read and process messages from server if (connected > -1) {
// read and process messages ...
}
// keep trying to establish connection to the server
// up to a maximum number of attempts } while (connected < 0 && count < MAX_ATTEMPTS);
// close socket and return success or failure ...
}
Example 2
For this example the method isReorderNeeded as 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 code)
Example Language: Java
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) {
// 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 code)
Example Language: Java
public boolean isReorderNeeded(String bookISBN, int rateSold) {
Chain: an integer overflow (CWE-190) in the image size calculation causes an infinite loop (CWE-835) which sequentially allocates buffers without limits (CWE-1325) until the stack is full.
Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
Nature
Type
ID
Name
MemberOf
View - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).
[REF-62] Mark Dowd, John McDonald
and Justin Schuh. "The Art of Software Security Assessment". Chapter 7, "Looping Constructs", Page 327. 1st Edition. Addison Wesley. 2006.
Description
Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
