CWE

Common Weakness Enumeration

A community-developed list of SW & HW weaknesses that can become vulnerabilities

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Home > CWE List > CWE- Individual Dictionary Definition (4.14)  
ID

CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')

Weakness ID: 835
Vulnerability Mapping: ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities
Abstraction: BaseBase - 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.
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+ Description
The product 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
Section HelpThis table 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)
NatureTypeIDName
ChildOfClassClass - 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.834Excessive Iteration
CanFollowBaseBase - 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.1322Use of Blocking Code in Single-threaded, Non-blocking Context
Section HelpThis table 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 "Software Development" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.438Behavioral Problems
Section HelpThis table 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 "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
NatureTypeIDName
ChildOfClassClass - 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.834Excessive Iteration
+ Applicable Platforms
Section HelpThis listing shows 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.

Languages

Class: Not Language-Specific (Undetermined Prevalence)

+ Common Consequences
Section HelpThis table 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.
ScopeImpactLikelihood
Availability

Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Amplification

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:
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:
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 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 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) {

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 code)
Example Language: Java 
public boolean isReorderNeeded(String bookISBN, int rateSold) {
...

// validate rateSold variable
if (rateSold < 1) {
return isReorder;
}

...
}
+ Observed Examples
ReferenceDescription
Chain: an operating system does not properly process malformed Open Shortest Path First (OSPF) Type/Length/Value Identifiers (TLV) (CWE-703), which can cause the process to enter an infinite loop (CWE-835)
A Python machine communication platform did not account for receiving a malformed packet with a null size, causing the receiving function to never update the message buffer and be caught in an infinite loop.
Chain: off-by-one error (CWE-193) leads to infinite loop (CWE-835) using invalid hex-encoded characters.
Chain: self-referential values in recursive definitions lead to infinite loop.
NULL UDP packet is never cleared from a queue, leading to infinite loop.
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]"
Floating point conversion routine cycles back and forth between two different values.
Floating point conversion routine cycles back and forth between two different values.
Chain: improperly clearing a pointer in a linked list leads to infinite loop.
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.
Chain: A denial of service may be caused by an uninitialized variable (CWE-457) allowing an infinite loop (CWE-835) resulting from a connection to an unresponsive server.
+ Memberships
Section HelpThis 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.
NatureTypeIDName
MemberOfViewView - 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).884CWE Cross-section
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1131CISQ Quality Measures (2016) - Security
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1306CISQ Quality Measures - Reliability
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1308CISQ Quality Measures - Security
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1410Comprehensive Categorization: Insufficient Control Flow Management
+ Vulnerability Mapping Notes

Usage: ALLOWED

(this CWE ID could be used to map to real-world vulnerabilities)

Reason: Acceptable-Use

Rationale:

This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.

Comments:

Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
OMG ASCSMASCSM-CWE-835
+ References
[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.
[REF-962] Object Management Group (OMG). "Automated Source Code Security Measure (ASCSM)". ASCSM-CWE-835. 2016-01. <http://www.omg.org/spec/ASCSM/1.0/>.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2011-03-22
(CWE 1.12, 2011-03-30)
CWE Content TeamMITRE
+ Modifications
Modification DateModifierOrganization
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings
2017-11-08CWE Content TeamMITRE
updated Demonstrative_Examples
2019-01-03CWE Content TeamMITRE
updated References, Relationships, Taxonomy_Mappings
2019-06-20CWE Content TeamMITRE
updated Relationships
2020-02-24CWE Content TeamMITRE
updated Relationships
2020-08-20CWE Content TeamMITRE
updated Relationships
2020-12-10CWE Content TeamMITRE
updated Observed_Examples, Relationships
2021-03-15CWE Content TeamMITRE
updated Observed_Examples
2021-07-20CWE Content TeamMITRE
updated Observed_Examples
2023-01-31CWE Content TeamMITRE
updated Description, Observed_Examples
2023-04-27CWE Content TeamMITRE
updated Relationships
2023-06-29CWE Content TeamMITRE
updated Mapping_Notes
2023-10-26CWE Content TeamMITRE
updated Observed_Examples
2024-02-29
(CWE 4.14, 2024-02-29)
CWE Content TeamMITRE
updated Demonstrative_Examples
Page Last Updated: February 29, 2024