CWE-539 Variant Incomplete

Use of Persistent Cookies Containing Sensitive Information

This vulnerability occurs when a web application stores sensitive data, like authentication details or personal information, within persistent cookies that remain on a user's device.

Definition

What is CWE-539?

This vulnerability occurs when a web application stores sensitive data, like authentication details or personal information, within persistent cookies that remain on a user's device.
Cookies are small pieces of data set by a web application and stored locally in a user's browser. While they are essential for maintaining state—like keeping a user logged in or remembering site preferences—they become a security risk when sensitive information is written directly into a cookie that is saved to disk. Unlike session cookies, which are deleted when the browser closes, persistent cookies remain on the hard drive for a defined period, making the sensitive data they contain accessible long-term. Storing sensitive data such as usernames, passwords, session tokens, or personal details in a persistent cookie exposes it to theft or misuse. Attackers can extract these cookies from browser files or through cross-site scripting (XSS) attacks, potentially leading to account takeover or privacy violations. Developers should instead use persistent cookies only for non-sensitive identifiers, storing the actual sensitive data securely on the server side where it can be properly protected.
Real-world impact

Real-world CVEs caused by CWE-539

No public CVE references are linked to this CWE in MITRE's catalog yet.

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-539

  • Architecture and Design Do not store sensitive information in persistent cookies.
Detection signals

How to detect CWE-539

Automated Static Analysis High

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.)

Plexicus auto-fix

Plexicus auto-detects CWE-539 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-539?

This vulnerability occurs when a web application stores sensitive data, like authentication details or personal information, within persistent cookies that remain on a user's device.

How serious is CWE-539?

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-539?

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

How can I prevent CWE-539?

Do not store sensitive information in persistent cookies.

How does Plexicus detect and fix CWE-539?

Plexicus's SAST engine matches the data-flow signature for CWE-539 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-539?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/539.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-539

CWE-552 Parent

Files or Directories Accessible to External Parties

This vulnerability occurs when an application exposes files or directories to users who shouldn't have access to them.

CWE-219 Sibling

Storage of File with Sensitive Data Under Web Root

This vulnerability occurs when an application saves sensitive files, such as configuration data or private keys, inside the web server's…

CWE-220 Sibling

Storage of File With Sensitive Data Under FTP Root

This vulnerability occurs when an application saves sensitive files, such as configuration or user data, within the directory served by an…

CWE-527 Sibling

Exposure of Version-Control Repository to an Unauthorized Control Sphere

This vulnerability occurs when a version control repository, like Git or SVN, is accidentally placed in a location accessible to…

CWE-528 Sibling

Exposure of Core Dump File to an Unauthorized Control Sphere

This vulnerability occurs when an application creates a core dump file (a snapshot of memory at the time of a crash) and places it in a…

CWE-529 Sibling

Exposure of Access Control List Files to an Unauthorized Control Sphere

This vulnerability occurs when an application stores sensitive access control list (ACL) files in a location that is accessible to…

CWE-530 Sibling

Exposure of Backup File to an Unauthorized Control Sphere

This vulnerability occurs when backup or temporary files are stored in locations that unauthorized users can access, such as web…

CWE-553 Sibling

Command Shell in Externally Accessible Directory

This vulnerability occurs when a command shell script is placed in a web-accessible directory, such as /cgi-bin/. Attackers can directly…

Resources

Further reading

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