CWE-523 Base Incomplete

Unprotected Transport of Credentials

This vulnerability occurs when a login page or authentication system transmits user credentials (like usernames and passwords) over a network without proper encryption, exposing them to interception.

Definition

What is CWE-523?

This vulnerability occurs when a login page or authentication system transmits user credentials (like usernames and passwords) over a network without proper encryption, exposing them to interception.
When credentials travel from a user's browser to your server without encryption, they are sent in plain text. Attackers on the same network can easily intercept this data using simple packet sniffing tools, leading directly to account compromise. This is a fundamental failure to protect the most sensitive part of the user session during its most vulnerable moment—transit. To prevent this, you must enforce the use of strong, modern encryption for all authentication traffic. Always use HTTPS (TLS/SSL) for your entire login process and application, never falling back to HTTP for any requests containing credentials. Additionally, implement HTTP Strict Transport Security (HSTS) to instruct browsers to always use a secure connection, preventing accidental data leakage.
Real-world impact

Real-world CVEs caused by CWE-523

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-523

  • Operation / System Configuration Enforce SSL use for the login page or any page used to transmit user credentials or other sensitive information. Even if the entire site does not use SSL, it MUST use SSL for login. Additionally, to help prevent phishing attacks, make sure that SSL serves the login page. SSL allows the user to verify the identity of the server to which they are connecting. If the SSL serves login page, the user can be certain they are talking to the proper end system. A phishing attack would typically redirect a user to a site that does not have a valid trusted server certificate issued from an authorized supplier.
Detection signals

How to detect CWE-523

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

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Frequently asked questions

Frequently asked questions

What is CWE-523?

This vulnerability occurs when a login page or authentication system transmits user credentials (like usernames and passwords) over a network without proper encryption, exposing them to interception.

How serious is CWE-523?

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-523?

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

How can I prevent CWE-523?

Enforce SSL use for the login page or any page used to transmit user credentials or other sensitive information. Even if the entire site does not use SSL, it MUST use SSL for login. Additionally, to help prevent phishing attacks, make sure that SSL serves the login page. SSL allows the user to verify the identity of the server to which they are connecting. If the SSL serves login page, the user can be certain they are talking to the proper end system. A phishing attack would typically redirect…

How does Plexicus detect and fix CWE-523?

Plexicus's SAST engine matches the data-flow signature for CWE-523 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-523?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/523.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-523

CWE-522 Parent

Insufficiently Protected Credentials

This vulnerability occurs when an application handles sensitive credentials like passwords or API keys in an insecure way, making them…

CWE-256 Sibling

Plaintext Storage of a Password

This vulnerability occurs when an application stores user passwords as readable text instead of using secure, one-way hashing. This…

CWE-257 Sibling

Storing Passwords in a Recoverable Format

This vulnerability occurs when an application stores user passwords in a format that can be easily reversed or decrypted back to their…

CWE-260 Sibling

Password in Configuration File

This vulnerability occurs when an application stores sensitive passwords directly within a configuration file, making them easily readable…

CWE-261 Sibling

Weak Encoding for Password

Using simple encoding like Base64 to hide a password provides no real security, as it can be easily reversed.

CWE-549 Sibling

Missing Password Field Masking

This vulnerability occurs when an application fails to hide password characters as they are typed, making them visible to anyone who can…

CWE-312 Peer

Cleartext Storage of Sensitive Information

This vulnerability occurs when an application stores sensitive data like passwords, credit card numbers, or personal information in plain…

Resources

Further reading

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