Summary

I spotted a buffer overflow vulnerability at the following location in the Zephyr STM32 Crypto driver source code:
https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/crypto/crypto_stm32.c

Details

Buffer overflow due to ineffective assert check in /drivers/crypto/crypto_stm32.c:

static void copy_reverse_words(uint8_t *dst_buf, int dst_len,
			       uint8_t *src_buf, int src_len)
{
	int i;

	__ASSERT_NO_MSG(dst_len >= src_len); /* VULN: assert */
	__ASSERT_NO_MSG((dst_len % 4) == 0);

	memcpy(dst_buf, src_buf, src_len); /* VULN: buffer overflow */
	for (i = 0; i < dst_len; i += sizeof(uint32_t)) {
		sys_mem_swap(&dst_buf[i], sizeof(uint32_t));
	}
}

The function copy_reverse_words() is called in a few locations that might be problematic, because src_len might be attacker-controlled:

• crypto_stm32_ctr_encrypt()
• crypto_stm32_ctr_decrypt()
• crypto_stm32_session_setup()

PoC

I haven't tried to reproduce these potential vulnerabilities against a live install of the Zephyr OS.

Impact

If the unchecked length above is confirmed to be attacker-controlled and if input crosses a security boundary, the impact of the buffer overflow vulnerability could range from denial of service to arbitrary code execution.

Patches

main: #61839