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A02:2021 – Cryptographic Failures icon


CWEs Mapped Max Incidence Rate Avg Incidence Rate Avg Weighted Exploit Avg Weighted Impact Max Coverage Avg Coverage Total Occurrences Total CVEs
29 46.44% 4.49% 7.29 6.81 79.33% 34.85% 233,788 3,075


Shifting up one position to #2, previously known as Sensitive Data Exposure, which is more of a broad symptom rather than a root cause, the focus is on failures related to cryptography (or lack thereof). Which often lead to exposure of sensitive data. Notable Common Weakness Enumerations (CWEs) included are CWE-259: Use of Hard-coded Password, CWE-327: Broken or Risky Crypto Algorithm, and CWE-331 Insufficient Entropy.


The first thing is to determine the protection needs of data in transit and at rest. For example, passwords, credit card numbers, health records, personal information, and business secrets require extra protection, mainly if that data falls under privacy laws, e.g., EU's General Data Protection Regulation (GDPR), or regulations, e.g., financial data protection such as PCI Data Security Standard (PCI DSS). For all such data:

  • Is any data transmitted in clear text? This concerns protocols such as HTTP, SMTP, FTP also using TLS upgrades like STARTTLS. External internet traffic is hazardous. Verify all internal traffic, e.g., between load balancers, web servers, or back-end systems.

  • Are any old or weak cryptographic algorithms or protocols used either by default or in older code?

  • Are default crypto keys in use, weak crypto keys generated or re-used, or is proper key management or rotation missing? Are crypto keys checked into source code repositories?

  • Is encryption not enforced, e.g., are any HTTP headers (browser) security directives or headers missing?

  • Is the received server certificate and the trust chain properly validated?

  • Are initialization vectors ignored, reused, or not generated sufficiently secure for the cryptographic mode of operation? Is an insecure mode of operation such as ECB in use? Is encryption used when authenticated encryption is more appropriate?

  • Are passwords being used as cryptographic keys in absence of a password base key derivation function?

  • Is randomness used for cryptographic purposes that was not designed to meet cryptographic requirements? Even if the correct function is chosen, does it need to be seeded by the developer, and if not, has the developer over-written the strong seeding functionality built into it with a seed that lacks sufficient entropy/unpredictability?

  • Are deprecated hash functions such as MD5 or SHA1 in use, or are non-cryptographic hash functions used when cryptographic hash functions are needed?

  • Are deprecated cryptographic padding methods such as PKCS number 1 v1.5 in use?

  • Are cryptographic error messages or side channel information exploitable, for example in the form of padding oracle attacks?

See ASVS Crypto (V7), Data Protection (V9), and SSL/TLS (V10)

How to Prevent

Do the following, at a minimum, and consult the references:

  • Classify data processed, stored, or transmitted by an application. Identify which data is sensitive according to privacy laws, regulatory requirements, or business needs.

  • Don't store sensitive data unnecessarily. Discard it as soon as possible or use PCI DSS compliant tokenization or even truncation. Data that is not retained cannot be stolen.

  • Make sure to encrypt all sensitive data at rest.

  • Ensure up-to-date and strong standard algorithms, protocols, and keys are in place; use proper key management.

  • Encrypt all data in transit with secure protocols such as TLS with forward secrecy (FS) ciphers, cipher prioritization by the server, and secure parameters. Enforce encryption using directives like HTTP Strict Transport Security (HSTS).

  • Disable caching for response that contain sensitive data.

  • Apply required security controls as per the data classification.

  • Do not use legacy protocols such as FTP and SMTP for transporting sensitive data.

  • Store passwords using strong adaptive and salted hashing functions with a work factor (delay factor), such as Argon2, scrypt, bcrypt or PBKDF2.

  • Initialization vectors must be chosen appropriate for the mode of operation. For many modes, this means using a CSPRNG (cryptographically secure pseudo random number generator). For modes that require a nonce, then the initialization vector (IV) does not need a CSPRNG. In all cases, the IV should never be used twice for a fixed key.

  • Always use authenticated encryption instead of just encryption.

  • Keys should be generated cryptographically randomly and stored in memory as byte arrays. If a password is used, then it must be converted to a key via an appropriate password base key derivation function.

  • Ensure that cryptographic randomness is used where appropriate, and that it has not been seeded in a predictable way or with low entropy. Most modern APIs do not require the developer to seed the CSPRNG to get security.

  • Avoid deprecated cryptographic functions and padding schemes, such as MD5, SHA1, PKCS number 1 v1.5 .

  • Verify independently the effectiveness of configuration and settings.

Example Attack Scenarios

Scenario #1: An application encrypts credit card numbers in a database using automatic database encryption. However, this data is automatically decrypted when retrieved, allowing a SQL injection flaw to retrieve credit card numbers in clear text.

Scenario #2: A site doesn't use or enforce TLS for all pages or supports weak encryption. An attacker monitors network traffic (e.g., at an insecure wireless network), downgrades connections from HTTPS to HTTP, intercepts requests, and steals the user's session cookie. The attacker then replays this cookie and hijacks the user's (authenticated) session, accessing or modifying the user's private data. Instead of the above they could alter all transported data, e.g., the recipient of a money transfer.

Scenario #3: The password database uses unsalted or simple hashes to store everyone's passwords. A file upload flaw allows an attacker to retrieve the password database. All the unsalted hashes can be exposed with a rainbow table of pre-calculated hashes. Hashes generated by simple or fast hash functions may be cracked by GPUs, even if they were salted.


List of Mapped CWEs

CWE-261 Weak Encoding for Password

CWE-296 Improper Following of a Certificate's Chain of Trust

CWE-310 Cryptographic Issues

CWE-319 Cleartext Transmission of Sensitive Information

CWE-321 Use of Hard-coded Cryptographic Key

CWE-322 Key Exchange without Entity Authentication

CWE-323 Reusing a Nonce, Key Pair in Encryption

CWE-324 Use of a Key Past its Expiration Date

CWE-325 Missing Required Cryptographic Step

CWE-326 Inadequate Encryption Strength

CWE-327 Use of a Broken or Risky Cryptographic Algorithm

CWE-328 Reversible One-Way Hash

CWE-329 Not Using a Random IV with CBC Mode

CWE-330 Use of Insufficiently Random Values

CWE-331 Insufficient Entropy

CWE-335 Incorrect Usage of Seeds in Pseudo-Random Number Generator(PRNG)

CWE-336 Same Seed in Pseudo-Random Number Generator (PRNG)

CWE-337 Predictable Seed in Pseudo-Random Number Generator (PRNG)

CWE-338 Use of Cryptographically Weak Pseudo-Random Number Generator(PRNG)

CWE-340 Generation of Predictable Numbers or Identifiers

CWE-347 Improper Verification of Cryptographic Signature

CWE-523 Unprotected Transport of Credentials

CWE-720 OWASP Top Ten 2007 Category A9 - Insecure Communications

CWE-757 Selection of Less-Secure Algorithm During Negotiation('Algorithm Downgrade')

CWE-759 Use of a One-Way Hash without a Salt

CWE-760 Use of a One-Way Hash with a Predictable Salt

CWE-780 Use of RSA Algorithm without OAEP

CWE-818 Insufficient Transport Layer Protection

CWE-916 Use of Password Hash With Insufficient Computational Effort