CWE-837 Base Incomplete

Improper Enforcement of a Single, Unique Action

This vulnerability occurs when a system fails to properly prevent users from repeating an action that should only be performed once, such as submitting a vote, finalizing a purchase, or requesting a…

Definition

What is CWE-837?

This vulnerability occurs when a system fails to properly prevent users from repeating an action that should only be performed once, such as submitting a vote, finalizing a purchase, or requesting a refund.
Many applications are designed to allow specific one-time actions, like casting a ballot, completing a transaction, or applying a coupon. When the system doesn't correctly track and enforce this single-use limitation, it creates a logic flaw that attackers can exploit. For example, in an e-commerce system, a user might bypass purchase limits or repeatedly apply a single-use discount code, leading to financial loss or inventory disruption. From a security perspective, this weakness directly undermines business rules and data integrity. An attacker could stuff a ballot in a voting app, repeatedly withdraw funds in a banking system, or spam a registration form to exhaust resources. The impact ranges from skewed analytics and unfair outcomes to significant revenue loss or system abuse, making robust single-action enforcement a critical requirement for both security and functional correctness.
Real-world impact

Real-world CVEs caused by CWE-837

  • CVE-2008-0294

    Ticket-booking web application allows a user to lock a seat more than once.

  • CVE-2005-4051

    CMS allows people to rate downloads by voting more than once.

  • CVE-2002-216

    Polling software allows people to vote more than once by setting a cookie.

  • CVE-2003-1433

    Chain: lack of validation of a challenge key in a game allows a player to register multiple times and lock other players out of the game.

  • CVE-2002-1018

    Library feature allows attackers to check out the same e-book multiple times, preventing other users from accessing copies of the e-book.

  • CVE-2009-2346

    Protocol implementation allows remote attackers to cause a denial of service (call-number exhaustion) by initiating many message exchanges.

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 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.

Vulnerable pseudo 
// 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

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-837

  • 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-837

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-837 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.

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Frequently asked questions

Frequently asked questions

What is CWE-837?

This vulnerability occurs when a system fails to properly prevent users from repeating an action that should only be performed once, such as submitting a vote, finalizing a purchase, or requesting a refund.

How serious is CWE-837?

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-837?

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

How can I prevent CWE-837?

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-837?

Plexicus's SAST engine matches the data-flow signature for CWE-837 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-837?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/837.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-837

CWE-799 Parent

Improper Control of Interaction Frequency

This vulnerability occurs when an application fails to properly restrict how often or how many times a user or automated system can…

CWE-307 Sibling

Improper Restriction of Excessive Authentication Attempts

This vulnerability occurs when an application fails to properly limit how many times someone can attempt to log in or verify their…

Resources

Further reading

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