Sensitive Information in Resource Not Removed Before Reuse

What is CWE-226?

Trajeto do atacante passo a passo

1. 1

   This example shows how an attacker can take advantage of an incorrect state transition.

2. 2

   Suppose a device is transitioning from state A to state B. During state A, it can read certain private keys from the hidden fuses that are only accessible in state A but not in state B. The device reads the keys, performs operations using those keys, then transitions to state B, where those private keys should no longer be accessible.

3. 3

   After the transition to state B, even though the private keys are no longer accessible directly from the fuses in state B, they can be accessed indirectly by reading the memory that contains the private keys.

4. 4

   The following code calls realloc() on a buffer containing sensitive data:

5. 5

   There is an attempt to scrub the sensitive data from memory, but realloc() is used, so it could return a pointer to a different part of memory. The memory that was originally allocated for cleartext_buffer could still contain an uncleared copy of the data.

How to prevent CWE-226

• Architecture and Design / Implementation During critical state transitions, information not needed in the next state should be removed or overwritten with fixed patterns (such as all 0's) or random data, before the transition to the next state.
• Architecture and Design / Implementation When releasing, de-allocating, or deleting a resource, overwrite its data and relevant metadata with fixed patterns or random data. Be cautious about complex resource types whose underlying representation might be non-contiguous or change at a low level, such as how a file might be split into different chunks on a file system, even though "logical" file positions are contiguous at the application layer. Such resource types might require invocation of special modes or APIs to tell the underlying operating system to perform the necessary clearing, such as SDelete (Secure Delete) on Windows, although the appropriate functionality might not be available at the application layer.

Frequently asked questions

Further reading

• MITRE — CWE-226 oficial https://cwe.mitre.org/data/definitions/226.html
• aes0_wrapper.sv https://github.com/HACK-EVENT/hackatdac21/blob/65d0ffdab7426da4509c98d62e163bcce642f651/piton/design/chip/tile/ariane/src/aes0/aes0_wrapper.sv#L84C2-L90C29
• Fix for aes0_wrapper https://github.com/HACK-EVENT/hackatdac21/blob/0034dff6852365a8c4e36590a47ea8b088d725ae/piton/design/chip/tile/ariane/src/aes0/aes0_wrapper.sv#L96C1-L102C16