CWE-327: Use of a Broken or Risky Cryptographic Algorithm

How it's found

Use of a Broken or Risky Cryptographic Algorithm describes a general pattern rather than a single fixed bug. Testers use a mix of static analysis and manual code review to find where a target's code matches this pattern, then confirm exploitability by hand.

Cryptographic algorithms are the methods by which data is scrambled to prevent observation or influence by unauthorized actors. Insecure cryptography can be exploited to expose sensitive information, modify data in unexpected ways, spoof identities of other users or devices, or other impacts. It is very difficult to produce a secure algorithm, and even high-profile algorithms by accomplished cryptographic experts have been broken. Well-known techniques exist to break or weaken various kinds of cryptography. Accordingly, there are a small number of well-understood and heavily studied algorithms that should be used by most products. Using a non-standard or known-insecure algorithm is dangerous because a determined adversary may be able to break the algorithm and compromise whatever data has been protected. Since the state of cryptography advances so rapidly, it is common for an algorithm to be considered "unsafe" even if it was once thought to be strong. This can happen when new attacks are discovered, or if computing power increases so much that the cryptographic algorithm no longer provides the amount of protection that was originally thought. For a number of reasons, this weakness is even more challenging to manage with hardware deployment of cryptographic algorithms as opposed to software implementation. First, if a flaw is discovered with hardware-implemented cryptography, the flaw cannot be fixed in most cases without a recall of the product, because hardware is not easily replaceable like software. Second, because the hardware product is expected to work for years, the adversary's computing power will only increase over time.

Vulnerable vs. safe

The manufacturer chooses a SHA1 hardware accelerator for to implement the scheme because it already has a working SHA1 Intellectual Property (IP) that the manufacturer had created and used earlier, so this reuse of IP saves design cost.

The manufacturer could have chosen a cryptographic solution that is recommended by the wide security community (including standard-setting bodies like NIST) and is not expected to be broken (or even better, weakened) within the reasonable life expectancy of the hardware product. In this case, the architects could have used SHA-2 or SHA-3, even if it meant that such choice would cost extra.

Consequences

• Read Application Data: The confidentiality of sensitive data may be compromised by the use of a broken or risky cryptographic algorithm.
• Modify Application Data: The integrity of sensitive data may be compromised by the use of a broken or risky cryptographic algorithm.
• Hide Activities: If the cryptographic algorithm is used to ensure the identity of the source of the data (such as digital signatures), then a broken algorithm will compromise this scheme and the source of the data cannot be proven.

Mitigations

• 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 [REF-1192]. 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: Ensure that the design allows one cryptographic algorithm to be replaced with another in the next generation or version. Where possible, use wrappers to make the interfaces uniform. This will make it easier to upgrade to stronger algorithms. With hardware, design the product at the Intellectual Property (IP) level so that one cryptographic algorithm can be replaced with another in the next generation of the hardware product.
• Architecture and Design: Carefully manage and protect cryptographic keys (see CWE-320). If the keys can be guessed or stolen, then the strength of the cryptography itself is irrelevant.
• Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482]. Industry-standard implementations will save development time and may be more likely to avoid errors that can occur during implementation of cryptographic algorithms. Consider the ESAPI Encryption feature.
• 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.

How TurboPentest tests for this

TurboPentest's automated black-box pentest actively probes for Use of a Broken or Risky Cryptographic Algorithm using testssl.sh to check the live TLS configuration for deprecated protocol versions (SSLv3, TLS 1.0/1.1) and broken ciphers, with no source code required. Connecting a GitHub repo adds white-box confirmation from IntegSec's Opengrep SAST rule pack, which carries 12 dedicated rules for this weakness.

Tools: testssl.sh

• ECB Mode
• Weak Cipher
• Weak Hash
• CBC Static IV
• Weak Cipher DES RC4
• Weak Hash MD5 SHA1
• Weak Cipher DES ECB
• Weak Hash MD5 SHA1
• Weak Cipher Algorithm
• Weak Hash Algorithm
• Weak Cipher DES ECB
• Weak Hash General

Frequently asked questions

Related CWEs

• Pillar weakness
  CWE-693: Protection Mechanism Failure
• Class weakness
  CWE-311: Missing Encryption of Sensitive Data
• Variant weakness
  CWE-14: Compiler Removal of Code to Clear Buffers
• Base weakness
  CWE-261: Weak Encoding for Password
• Variant weakness
  CWE-321: Use of Hard-coded Cryptographic Key
• Class weakness
  CWE-326: Inadequate Encryption Strength