CWE-834 Class Incomplete

Excessive Iteration

This vulnerability occurs when a program runs a loop too many times because it lacks proper limits on its iterations.

Definition

What is CWE-834?

This vulnerability occurs when a program runs a loop too many times because it lacks proper limits on its iterations.

When an attacker can control or influence the loop's conditions, they can force it to run far more times than intended. This quickly drains system resources like CPU cycles and memory, potentially causing slowdowns, service denial, or crashes. Even a loop that isn't technically infinite can be dangerous if each pass consumes significant resources. For developers, the core issue is trusting unvalidated input to control loop counters or termination logic. To prevent this, always enforce explicit, reasonable upper bounds on all iterative processes, especially those influenced by external data like user input, file contents, or network responses.

Real-world impact

Real-world CVEs caused by CWE-834

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]"

How attackers exploit it

Step-by-step attacker path

1
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.
2
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.
3
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.
4
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.

Vulnerable code example

Vulnerable C

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.

Vulnerable C

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);

Secure code example

Secure C

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.

Secure C

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);

What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.

Prevention checklist

How to prevent CWE-834

Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
Implementation Validate input at trust boundaries; use allowlists, not denylists.
Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
Operation Monitor logs for the runtime signals listed in the next section.

Detection signals

How to detect CWE-834

Dynamic Analysis with Manual Results Interpretation SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Fuzz Tester Framework-based Fuzzer Forced Path Execution

Manual Static Analysis - Source Code SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Focused Manual Spotcheck - Focused manual analysis of source Manual Source Code Review (not inspections)

Automated Static Analysis - Source Code High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Context-configured Source Code Weakness Analyzer

Architecture or Design Review High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

CWE-834

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Frequently asked questions

What is CWE-834?

This vulnerability occurs when a program runs a loop too many times because it lacks proper limits on its iterations.

How serious is CWE-834?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-834?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-834?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

How does Plexicus detect and fix CWE-834?

Plexicus's SAST engine matches the data-flow signature for CWE-834 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-834?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/834.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-834

CWE-691 Parent

Excessive Iteration

What is CWE-834?

Real-world CVEs caused by CWE-834

Step-by-step attacker path

Vulnerable C

Secure C

How to prevent CWE-834

How to detect CWE-834

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-834

Insufficient Control Flow Management

Unintended Reentrant Invocation of Non-reentrant Code Via Nested Calls

Sequence of Processor Instructions Leads to Unexpected Behavior

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Deployment of Wrong Handler

Missing Handler

Improper Synchronization

Always-Incorrect Control Flow Implementation

Incorrect Behavior Order

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`