CWE-606: Unchecked Input for Loop Condition

Code Examples & CVEs

Demonstrative Examples

The following example demonstrates the weakness.

BadC

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

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.

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).

BadC

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;                      }

Observed CVE Examples (1)

CVE-2025-32399

Chain: library for implementing Profinet devices does not check an input for a loop condition (CWE-606), allowing an infinite loop (CWE-835) via a crafted RPC packet

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Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-606 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-606, Unchecked Input for Loop Condition, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Unchecked Input for Loop Condition during Implementation

MITRE associates mitigation with Implementation; documented detection approaches include Automated Static Analysis; recorded impacts include DoS: Resource Consumption (CPU). Use these source-defined anchors to turn CWE-606 into implementation, review, and verification checks for the affected component.

CWE-606: Unchecked Input for Loop Condition — MITRE CWE

Triage CWE-606 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-606, Unchecked Input for Loop Condition, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-606

Apply MITRE's full root-cause mapping guidance when using CWE-606, Unchecked Input for Loop Condition. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-606 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-606, Unchecked Input for Loop Condition. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-606: Unchecked Input for Loop Condition?+

CWE-606: Unchecked Input for Loop Condition is a Common Weakness Enumeration (CWE) entry maintained by MITRE. 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.

What are the security consequences of Unchecked Input for Loop Condition?+

If exploited, CWE-606 (Unchecked Input for Loop Condition) it can compromise Availability, leading to outcomes such as DoS: Resource Consumption (CPU).

How do you prevent or mitigate Unchecked Input for Loop Condition?+

Recommended mitigations for CWE-606 include: Do not use user-controlled data for loop conditions. Perform input validation.

Which programming languages are affected by Unchecked Input for Loop Condition?+

CWE-606 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What are real-world examples of Unchecked Input for Loop Condition?+

MITRE documents real CVEs mapped to CWE-606, including CVE-2025-32399. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-606 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-606: Unchecked Input for Loop Condition

Technical Details

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Mitigation Strategies

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