CA5358: Do Not Use Unsafe Cipher Modes

Property	Value
Rule ID	CA5358
Title	Do Not Use Unsafe Cipher Modes
Category	Security
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 9	No

Cause

Use of one of the following unsafe encryption modes that is not approved:

• System.Security.Cryptography.CipherMode.ECB
• System.Security.Cryptography.CipherMode.OFB
• System.Security.Cryptography.CipherMode.CFB

Rule description

These modes are vulnerable to attacks and may cause exposure of sensitive information. For example, using ECB to encrypt a plaintext block always produces a same cipher text, so it can easily tell if two encrypted messages are identical. Using approved modes can avoid these unnecessary risks.

How to fix violations

• Use only approved modes (System.Security.Cryptography.CipherMode.CBC, System.Security.Cryptography.CipherMode.CTS).

When to suppress warnings

It's safe to suppress a warning from this rule if:

• Cryptography experts have reviewed and approved the cipher mode's usage.
• The referenced CipherMode isn't used for a cryptographic operation.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

C#

#pragma warning disable CA5358
// The code that's violating the rule is on this line.
#pragma warning restore CA5358

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

ini

[*.{cs,vb}]
dotnet_diagnostic.CA5358.severity = none

For more information, see How to suppress code analysis warnings.

Pseudo-code examples

Assign ECB to Mode property

C#

using System.Security.Cryptography;

class ExampleClass {
    private static void ExampleMethod () {
        RijndaelManaged rijn = new RijndaelManaged
        {
            Mode = CipherMode.ECB
        };
    }
}

Using the value ECB

C#

using System;
using System.Security.Cryptography;

class ExampleClass
{
    private static void ExampleMethod()
    {
        Console.WriteLine(CipherMode.ECB);
    }
}

Solution

C#

using System.Security.Cryptography;

class ExampleClass {
    private static void ExampleMethod () {
        RijndaelManaged rijn = new RijndaelManaged
        {
            Mode = CipherMode.CBC
        };
    }
}