CWE - CWE-606: Unchecked Input for Loop Condition (4.19.1)
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    CWE-606: Unchecked Input for Loop Condition

    Weakness ID: 606
    Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
    Abstraction: Base 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.
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    + Description
    The product does not properly check inputs that are used for loop conditions, potentially leading to a denial of service or other consequences because of excessive looping.
    + 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.
    Impact Details

    DoS: Resource Consumption (CPU)

    		Scope: Availability

    + Potential Mitigations
    Phase(s) Mitigation

    Implementation
    Do not use user-controlled data for loop conditions.

    Implementation
    Perform input validation.
    + Relationships
    Section Help This 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" (View-1000)
    Nature Type ID Name
    ChildOf Base 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. 1284 Improper Validation of Specified Quantity in Input
    CanPrecede Class 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. 834 Excessive Iteration
    + Relevant to the view "Software Development" (View-699)
    Nature Type ID Name
    MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 1215 Data Validation Issues
    + Modes Of Introduction
    Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
    Phase Note
    Implementation
    + 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)

    + Demonstrative Examples

    Example 1


    The following example demonstrates the weakness.

    (bad code)
    Example Language: C 
    void iterate(int n){
    int i;
    for (i = 0; i < n; i++){
    foo();
    }
    }
    void iterateFoo()
    {
    unsigned int num;
    scanf("%u",&num);
    iterate(num);
    }


    Example 2


    In the following C/C++ example the method processMessageFromSocket() will get a message from a socket, placed into a buffer, and will parse the contents of the buffer into a structure that contains the message length and the message body. A for loop is used to copy the message body into a local character string which will be passed to another method for processing.

    (bad code)
    Example Language: C 
    int processMessageFromSocket(int socket) {
    int success;

    char buffer[BUFFER_SIZE];
    char message[MESSAGE_SIZE];

    // get message from socket and store into buffer

    //Ignoring possibliity that buffer > BUFFER_SIZE
    if (getMessage(socket, buffer, BUFFER_SIZE) > 0) {

    // place contents of the buffer into message structure
    ExMessage *msg = recastBuffer(buffer);

    // copy message body into string for processing
    int index;
    for (index = 0; index < msg->msgLength; index++) {
    message[index] = msg->msgBody[index];
    }
    message[index] = '\0';

    // process message
    success = processMessage(message);
    }
    return success;
    }

    However, the message length variable (msgLength) from the structure is used as the condition for ending the for loop without validating that msgLength accurately reflects the actual length of the message body (CWE-606). If msgLength indicates a length that is longer than the size of a message body (CWE-130), then this can result in a buffer over-read by reading past the end of the buffer (CWE-126).



    + Weakness Ordinalities
    Ordinality Description
    Primary
    (where the weakness exists independent of other weaknesses)
    + Detection Methods
    Method Details

    Automated Static Analysis
    Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

    Effectiveness: High
    + 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.
    Nature Type ID Name
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 738 CERT C Secure Coding Standard (2008) Chapter 5 - Integers (INT)
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 872 CERT C++ Secure Coding Section 04 - Integers (INT)
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 994 SFP Secondary Cluster: Tainted Input to Variable
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1131 CISQ Quality Measures (2016) - Security
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1308 CISQ Quality Measures - Security
    MemberOf ViewView - 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). 1340 CISQ Data Protection Measures
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1406 Comprehensive Categorization: Improper Input Validation
    + Vulnerability Mapping Notes
    Usage ALLOWED
    (this CWE ID may 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 Name Node ID Fit Mapped Node Name
    Software Fault Patterns SFP25 Tainted input to variable
    OMG ASCSM ASCSM-CWE-606
    + 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-606. 2016-01.
    <http://www.omg.org/spec/ASCSM/1.0/>.
    + Content History
    + Submissions
    Submission Date Submitter Organization
    2007-05-07
    (CWE Draft 6, 2007-05-07)     		Anonymous Tool Vendor (under NDA)
    + Modifications
    Modification Date Modifier Organization
    2025-12-11
    (CWE 4.19, 2025-12-11)     		CWE Content Team MITRE
    updated Applicable_Platforms, Weakness_Ordinalities
    2025-09-09
    (CWE 4.18, 2025-09-09)     		CWE Content Team MITRE
    updated Demonstrative_Examples
    2023-06-29 CWE Content Team MITRE
    updated Mapping_Notes
    2023-04-27 CWE Content Team MITRE
    updated Detection_Factors, Relationships
    2020-12-10 CWE Content Team MITRE
    updated Relationships
    2020-08-20 CWE Content Team MITRE
    updated Relationships
    2020-06-25 CWE Content Team MITRE
    updated Demonstrative_Examples, Description, Relationships
    2020-02-24 CWE Content Team MITRE
    updated Relationships
    2019-01-03 CWE Content Team MITRE
    updated References, Relationships, Taxonomy_Mappings
    2017-11-08 CWE Content Team MITRE
    updated Demonstrative_Examples, Taxonomy_Mappings
    2014-07-30 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2012-10-30 CWE Content Team MITRE
    updated Potential_Mitigations
    2012-05-11 CWE Content Team MITRE
    updated References, Relationships
    2011-09-13 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2011-06-01 CWE Content Team MITRE
    updated Common_Consequences
    2011-03-29 CWE Content Team MITRE
    updated Demonstrative_Examples, Relationships
    2009-10-29 CWE Content Team MITRE
    updated Relationships
    2009-05-27 CWE Content Team MITRE
    updated Demonstrative_Examples
    2008-11-24 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2008-09-08 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings, Type
    2008-07-01 Eric Dalci Cigital
    updated Potential_Mitigations, Time_of_Introduction
    Page Last Updated: January 21, 2026