Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-462 Variant Incomplete
Duplicate Key in Associative List (Alist)
This vulnerability occurs when an associative list (alist) contains duplicate keys, which can cause unexpected behavior when software incorrectly handles or interprets these duplicates.
Definition
What is CWE-462?
This vulnerability occurs when an associative list (alist) contains duplicate keys, which can cause unexpected behavior when software incorrectly handles or interprets these duplicates.
While a duplicate key could theoretically be used to implement a constant-time replacement function in a properly designed associative list, this pattern is inherently risky. In practice, duplicates are far more likely to be inserted accidentally due to programming errors, leading to ambiguous data states where it's unclear whether the duplicate was intentional or a mistake.
Because this ambiguity creates a significant source of bugs and security flaws—such as data corruption, incorrect lookups, or logic errors—best practice dictates that associative lists should enforce key uniqueness. Developers should prevent duplicate keys at the point of insertion or validate the list to ensure all keys are unique, rather than relying on downstream code to interpret the duplicates correctly.
Real-world impact
Real-world CVEs caused by CWE-462
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 Python
The following code adds data to a list and then attempts to sort the data.
alist = []
while (foo()): #now assume there is a string data with a key basename
queue.append(basename,data)
queue.sort() 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-462
- Architecture and Design Use a hash table instead of an alist.
- Architecture and Design Use an alist which checks the uniqueness of hash keys with each entry before inserting the entry.
Detection signals
How to detect CWE-462
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.
CWE-462
Don't catalog this weakness. Prove it's reachable.
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-462?
How serious is CWE-462?
What languages or platforms are affected by CWE-462?
How can I prevent CWE-462?
How does Plexicus detect and fix CWE-462?
Where can I learn more about CWE-462?
Frequently asked questions
What is CWE-462?
This vulnerability occurs when an associative list (alist) contains duplicate keys, which can cause unexpected behavior when software incorrectly handles or interprets these duplicates.
How serious is CWE-462?
MITRE rates the likelihood of exploit as Low — exploitation is uncommon, but the weakness should still be fixed when discovered.
What languages or platforms are affected by CWE-462?
MITRE lists the following affected platforms: C, C++, Java, C#.
How can I prevent CWE-462?
Use a hash table instead of an alist. Use an alist which checks the uniqueness of hash keys with each entry before inserting the entry.
How does Plexicus detect and fix CWE-462?
Plexicus's SAST engine matches the data-flow signature for CWE-462 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-462?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/462.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-462
CWE-694 Parent
Use of Multiple Resources with Duplicate Identifier
This vulnerability occurs when a system uses multiple resources that can share the same identifier, even though the application logic…
CWE-102 Sibling
Struts: Duplicate Validation Forms
This vulnerability occurs when an application defines multiple Struts validation forms with identical names. The framework then…
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