CWE-311 Class Draft High likelihood

Missing Encryption of Sensitive Data

This vulnerability occurs when an application stores or sends sensitive information without first encrypting it, leaving the data exposed.

Definition

What is CWE-311?

This vulnerability occurs when an application stores or sends sensitive information without first encrypting it, leaving the data exposed.
Sensitive data like passwords, financial details, personal identification numbers, or authentication tokens must be encrypted both at rest (in databases, logs, or files) and in transit (over networks). When developers skip this step, any attacker who gains access to the storage or can intercept the network traffic can read the information directly, leading to immediate data breaches, identity theft, or system compromise. Preventing this requires a proactive security mindset. Always use strong, standard encryption algorithms (like AES for storage and TLS for transmission) and manage encryption keys securely. Treat any data that could harm users or your organization if exposed as 'sensitive' and encrypt it by default, rather than trying to decide case-by-case. Regularly audit your code and configurations to ensure no critical data flows or persists in plaintext.
Vulnerability Diagram CWE-311
Missing Encryption of Sensitive Data App SSN, card #, token stored as-is Disk / DB name | ssn alice| 123-45-6789 bob | 987-65-4321 eve | 555-55-5555 Theft of disk backup leak, stolen laptop, misconfigured S3 → data is plain Sensitive fields are written without encryption-at-rest.
Real-world impact

Real-world CVEs caused by CWE-311

  • CVE-2009-2272

    password and username stored in cleartext in a cookie

  • CVE-2009-1466

    password stored in cleartext in a file with insecure permissions

  • CVE-2009-0152

    chat program disables SSL in some circumstances even when the user says to use SSL.

  • CVE-2009-1603

    Chain: product uses an incorrect public exponent when generating an RSA key, which effectively disables the encryption

  • CVE-2009-0964

    storage of unencrypted passwords in a database

  • CVE-2008-6157

    storage of unencrypted passwords in a database

  • CVE-2008-6828

    product stores a password in cleartext in memory

  • CVE-2008-1567

    storage of a secret key in cleartext in a temporary file

How attackers exploit it

Step-by-step attacker path

  1. 1

    This code writes a user's login information to a cookie so the user does not have to login again later.

  2. 2

    The code stores the user's username and password in plaintext in a cookie on the user's machine. This exposes the user's login information if their computer is compromised by an attacker. Even if the user's machine is not compromised, this weakness combined with cross-site scripting (CWE-79) could allow an attacker to remotely copy the cookie.

  3. 3

    Also note this example code also exhibits Plaintext Storage in a Cookie (CWE-315).

  4. 4

    The following code attempts to establish a connection, read in a password, then store it to a buffer.

  5. 5

    While successful, the program does not encrypt the data before writing it to a buffer, possibly exposing it to unauthorized actors.

Vulnerable code example

Vulnerable PHP

This code writes a user's login information to a cookie so the user does not have to login again later.

Vulnerable PHP 
function persistLogin($username, $password){
  	$data = array("username" => $username, "password"=> $password);
  	setcookie ("userdata", $data);
  }
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-311

  • Requirements Clearly specify which data or resources are valuable enough that they should be protected by encryption. Require that any transmission or storage of this data/resource should use well-vetted encryption algorithms.
  • Architecture and Design Ensure that encryption is properly integrated into the system design, including but not necessarily limited to: - Encryption that is needed to store or transmit private data of the users of the system - Encryption that is needed to protect the system itself from unauthorized disclosure or tampering Identify the separate needs and contexts for encryption: - One-way (i.e., only the user or recipient needs to have the key). This can be achieved using public key cryptography, or other techniques in which the encrypting party (i.e., the product) does not need to have access to a private key. - Two-way (i.e., the encryption can be automatically performed on behalf of a user, but the key must be available so that the plaintext can be automatically recoverable by that user). This requires storage of the private key in a format that is recoverable only by the user (or perhaps by the operating system) in a way that cannot be recovered by others. Using threat modeling or other techniques, assume that data can be compromised through a separate vulnerability or weakness, and determine where encryption will be most effective. Ensure that data that should be private is not being inadvertently exposed using weaknesses such as insecure permissions (CWE-732). [REF-7]
  • Architecture and Design When there is a need to store or transmit sensitive data, use strong, up-to-date cryptographic algorithms to encrypt that data. Select a well-vetted algorithm that is currently considered to be strong by experts in the field, and use well-tested implementations. As with all cryptographic mechanisms, the source code should be available for analysis. For example, US government systems require FIPS 140-2 certification. Do not develop custom or private cryptographic algorithms. They will likely be exposed to attacks that are well-understood by cryptographers. Reverse engineering techniques are mature. If the algorithm can be compromised if attackers find out how it works, then it is especially weak. Periodically ensure that the cryptography has not become obsolete. Some older algorithms, once thought to require a billion years of computing time, can now be broken in days or hours. This includes MD4, MD5, SHA1, DES, and other algorithms that were once regarded as strong. [REF-267]
  • Architecture and Design Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
  • Implementation / Architecture and Design When using industry-approved techniques, use them correctly. Don't cut corners by skipping resource-intensive steps (CWE-325). These steps are often essential for preventing common attacks.
  • Implementation Use naming conventions and strong types to make it easier to spot when sensitive data is being used. When creating structures, objects, or other complex entities, separate the sensitive and non-sensitive data as much as possible.
Detection signals

How to detect CWE-311

Manual Analysis High

The characterizaton of sensitive data often requires domain-specific understanding, so manual methods are useful. However, manual efforts might not achieve desired code coverage within limited time constraints. Black box methods may produce artifacts (e.g. stored data or unencrypted network transfer) that require manual evaluation.

Automated Analysis

Automated measurement of the entropy of an input/output source may indicate the use or lack of encryption, but human analysis is still required to distinguish intentionally-unencrypted data (e.g. metadata) from sensitive data.

Manual Static Analysis - Binary or Bytecode SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Dynamic Analysis with Automated Results Interpretation SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Web Application Scanner Web Services Scanner Database Scanners

Dynamic Analysis with Manual Results Interpretation High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Network Sniffer ``` Cost effective for partial coverage: ``` Fuzz Tester Framework-based Fuzzer Automated Monitored Execution Man-in-the-middle attack tool

Manual Static Analysis - Source Code High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Focused Manual Spotcheck - Focused manual analysis of source Manual Source Code Review (not inspections)

Plexicus auto-fix

Plexicus auto-detects CWE-311 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.

Get a demo Try Plexicus free
Frequently asked questions

Frequently asked questions

What is CWE-311?

This vulnerability occurs when an application stores or sends sensitive information without first encrypting it, leaving the data exposed.

How serious is CWE-311?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-311?

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

How can I prevent CWE-311?

Clearly specify which data or resources are valuable enough that they should be protected by encryption. Require that any transmission or storage of this data/resource should use well-vetted encryption algorithms. Ensure that encryption is properly integrated into the system design, including but not necessarily limited to: - Encryption that is needed to store or transmit private data of the users of the system - Encryption that is needed to protect the system itself from unauthorized…

How does Plexicus detect and fix CWE-311?

Plexicus's SAST engine matches the data-flow signature for CWE-311 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-311?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/311.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-311

CWE-693 Parent

Protection Mechanism Failure

This weakness occurs when software either lacks a necessary security control, implements one that is too weak, or fails to activate an…

CWE-1039 Sibling

Inadequate Detection or Handling of Adversarial Input Perturbations in Automated Recognition Mechanism

This vulnerability occurs when a system uses automated AI or machine learning to classify complex inputs like images, audio, or text, but…

CWE-1248 Sibling

Semiconductor Defects in Hardware Logic with Security-Sensitive Implications

A security-critical hardware component contains physical flaws in its semiconductor material, which can cause it to malfunction and…

CWE-1253 Sibling

Incorrect Selection of Fuse Values

This vulnerability occurs when a hardware security fuse is incorrectly programmed to represent a 'secure' state as logic 0 (unblown). An…

CWE-1269 Sibling

Product Released in Non-Release Configuration

This vulnerability occurs when a product ships to customers while still configured with its pre-production or manufacturing settings,…

CWE-1278 Sibling

Missing Protection Against Hardware Reverse Engineering Using Integrated Circuit (IC) Imaging Techniques

This vulnerability occurs when hardware lacks safeguards against physical inspection, allowing attackers to extract sensitive data by…

CWE-1291 Sibling

Public Key Re-Use for Signing both Debug and Production Code

This vulnerability occurs when the same cryptographic key is used to sign both development/debug software builds and final production…

CWE-1318 Sibling

Missing Support for Security Features in On-chip Fabrics or Buses

This vulnerability occurs when the communication channels (fabrics or buses) within a chip lack built-in or enabled security features,…

CWE-1319 Sibling

Improper Protection against Electromagnetic Fault Injection (EM-FI)

This vulnerability occurs when a hardware device lacks sufficient shielding against electromagnetic interference, allowing attackers to…

Resources

Further reading

Ready when you are

Don't Let Security
Weigh You Down.

Stop choosing between AI velocity and security debt. Plexicus is the only platform that runs Vibe Coding Security and ASPM in parallel — one workflow, every codebase.

Get started free Book a demo