CWE-261 Base Incomplete

Weak Encoding for Password

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

Definition

What is CWE-261?

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

This weakness occurs when developers try to protect passwords stored in configuration files or application properties by encoding them with schemes like Base64, hex, or ROT13. While this obscures the password from casual viewing, it is not encryption. Any attacker who discovers the encoded string can trivially decode it back to the original plaintext password, offering no meaningful defense. True password protection requires strong, one-way cryptographic hashing with a salt, or using a dedicated secrets management solution. Encoding is a form of security through obscurity that creates a false sense of safety. Developers should treat any encoded secret as if it were plaintext, because for an attacker, it effectively is.

Real-world impact

Real-world CVEs caused by CWE-261

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

How attackers exploit it

Step-by-step attacker path

1
The following code reads a password from a properties file and uses the password to connect to a database.
2
This code will run successfully, but anyone with access to config.properties can read the value of password and easily determine that the value has been base 64 encoded. If a devious employee has access to this information, they can use it to break into the system.
3
The following code reads a password from the registry and uses the password to create a new network credential.
4
This code will run successfully, but anyone who has access to the registry key used to store the password can read the value of password. If a devious employee has access to this information, they can use it to break into the system.

Vulnerable code example

Vulnerable Java

The following code reads a password from a properties file and uses the password to connect to a database.

Vulnerable Java

...
  Properties prop = new Properties();
  prop.load(new FileInputStream("config.properties"));
  String password = Base64.decode(prop.getProperty("password"));
  DriverManager.getConnection(url, usr, password);
  ...

Secure code example

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-261

Passwords should be encrypted with keys that are at least 128 bits in length for adequate security.

Detection signals

How to detect CWE-261

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.)

CWE-261

Don't catalog this weakness. Prove it's reachable.

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Frequently asked questions

What is CWE-261?

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

How serious is CWE-261?

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-261?

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

How can I prevent CWE-261?

Passwords should be encrypted with keys that are at least 128 bits in length for adequate security.

How does Plexicus detect and fix CWE-261?

Plexicus's SAST engine matches the data-flow signature for CWE-261 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-261?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/261.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-261

CWE-522 Parent

Weak Encoding for Password

What is CWE-261?

Real-world CVEs caused by CWE-261

Step-by-step attacker path

Vulnerable Java

Secure pseudo

How to prevent CWE-261

How to detect CWE-261

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-261

Insufficiently Protected Credentials

Plaintext Storage of a Password

Storing Passwords in a Recoverable Format

Password in Configuration File

Unprotected Transport of Credentials

Missing Password Field Masking

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`