Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-773 Variant Incomplete
Missing Reference to Active File Descriptor or Handle
This vulnerability occurs when a program fails to keep track of open files or resources, preventing the system from properly closing and reclaiming them.
Definition
What is CWE-773?
This vulnerability occurs when a program fails to keep track of open files or resources, preventing the system from properly closing and reclaiming them.
When a file, network socket, or other system resource is opened, the operating system assigns it a unique identifier called a file descriptor or handle. If the software loses its reference to this identifier—for example, by overwriting a variable or exiting a scope without closing it—the resource remains allocated but unusable. This is often called a resource leak.
Over time, these unreleased resources accumulate. Since operating systems impose strict limits on the total number of file descriptors available per process, the application can eventually exhaust this pool. When all descriptors are consumed, the program will fail to open new files, establish network connections, or even crash, potentially causing a denial-of-service condition for itself and other processes on the system.
Real-world impact
Real-world CVEs caused by CWE-773
No public CVE references are linked to this CWE in MITRE's catalog yet.
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 pseudo
MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} 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-773
- Operation / Architecture and Design Use resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).
Detection signals
How to detect CWE-773
Run dynamic application security testing against the live endpoint.
Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.
Code review: flag any new code that handles input from this surface without using the validated framework helpers.
Plexicus auto-detects CWE-773 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-773?
How serious is CWE-773?
What languages or platforms are affected by CWE-773?
How can I prevent CWE-773?
How does Plexicus detect and fix CWE-773?
Where can I learn more about CWE-773?
Frequently asked questions
What is CWE-773?
This vulnerability occurs when a program fails to keep track of open files or resources, preventing the system from properly closing and reclaiming them.
How serious is CWE-773?
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-773?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-773?
Use resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged…
How does Plexicus detect and fix CWE-773?
Plexicus's SAST engine matches the data-flow signature for CWE-773 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-773?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/773.html. You can also reference OWASP and NIST documentation for adjacent guidance.
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