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.)
CWE-674 Class Draft
Uncontrolled Recursion
This vulnerability occurs when an application fails to limit how deeply a function can call itself. Without proper controls, this uncontrolled recursion can exhaust system resources like memory or…
Definition
What is CWE-674?
This vulnerability occurs when an application fails to limit how deeply a function can call itself. Without proper controls, this uncontrolled recursion can exhaust system resources like memory or stack space, leading to crashes or denial-of-service.
Uncontrolled recursion happens when a recursive function lacks a proper termination condition or depth limit. This allows it to run indefinitely or until it consumes all available stack memory, causing a stack overflow. Common triggers include processing deeply nested user input (like XML/JSON), complex graph traversals, or mathematical sequences without safety checks. Developers should always implement a maximum recursion depth or convert recursive logic to iterative loops for critical operations.
Detecting these flaws manually in a large codebase is challenging, as recursion paths can be complex. While SAST tools can identify the risky pattern, Plexicus uses AI to not only flag the issue but also generate specific, safe code fixes—such as adding depth counters or suggesting iterative alternatives—saving significant manual review and remediation time.
Real-world impact
Real-world CVEs caused by CWE-674
-
Deeply nested arrays trigger stack exhaustion.
-
Self-referencing pointers create infinite loop and resultant stack exhaustion.
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Javascript application accidentally changes input in a way that prevents a recursive call from detecting an exit condition.
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An attempt to recover a corrupted XML file infinite recursion protection counter was not always incremented missing the exit condition.
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USB-audio driver's descriptor code parsing allows unlimited recursion leading to stack exhaustion.
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 4
Iterate until the response leaks data, executes attacker code, or escalates privileges.
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.
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.
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-674
- Implementation Ensure an end condition will be reached under all logic conditions. The end condition may include testing against the depth of recursion and exiting with an error if the recursion goes too deep. The complexity of the end condition contributes to the effectiveness of this action.
- Implementation Increase the stack size.
Detection signals
How to detect CWE-674
CWE-674
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Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Frequently asked questions What is CWE-674?
How serious is CWE-674?
What languages or platforms are affected by CWE-674?
How can I prevent CWE-674?
How does Plexicus detect and fix CWE-674?
Where can I learn more about CWE-674?
Frequently asked questions
What is CWE-674?
This vulnerability occurs when an application fails to limit how deeply a function can call itself. Without proper controls, this uncontrolled recursion can exhaust system resources like memory or stack space, leading to crashes or denial-of-service.
How serious is CWE-674?
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-674?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-674?
Ensure an end condition will be reached under all logic conditions. The end condition may include testing against the depth of recursion and exiting with an error if the recursion goes too deep. The complexity of the end condition contributes to the effectiveness of this action. Increase the stack size.
How does Plexicus detect and fix CWE-674?
Plexicus's SAST engine matches the data-flow signature for CWE-674 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-674?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/674.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-674
CWE-834 Parent
Excessive Iteration
This vulnerability occurs when a program runs a loop too many times because it lacks proper limits on its iterations.
CWE-1322 Sibling
Use of Blocking Code in Single-threaded, Non-blocking Context
This vulnerability occurs when an application designed to be single-threaded and non-blocking, for performance and scalability,…
CWE-835 Sibling
Loop with Unreachable Exit Condition ('Infinite Loop')
An infinite loop occurs when a program's iteration logic contains an exit condition that can never be satisfied, causing the loop to run…
CWE-776 Child
Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
This vulnerability occurs when an XML parser allows Document Type Definitions (DTDs) to contain recursively defined entities without…
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