Hi,

I would like to report another potential vulnerability in the current version of RT-Thread. Please let me know if you plan to ask for a CVE ID in case the vulnerability is confirmed. I'm available if you need further clarifications.

Weak random source in RT-Thread rt_random driver

Summary

I noticed a weak random source at the following location in the RT-Thread rt_random driver source code:
https://github.com/RT-Thread/rt-thread/blob/master/components/drivers/misc/rt_random.c#L16-L28

Details

Weak random generator in the the calc_random() function:

static rt_uint16_t calc_random(void)
{
    seed = 214013L * seed   2531011L;
    return (seed >> 16) & 0x7FFF;   /* return bits 16~30 */
}

static rt_ssize_t random_read(rt_device_t dev, rt_off_t pos, void *buffer, rt_size_t size)
{
    rt_uint16_t rand = calc_random(); /* VULN: weak random source */
    ssize_t ret = sizeof(rand);
    rt_memcpy(buffer, &rand, ret);
    return ret;
}

Impact

If the reported weak random generator is used in a security context, such as cryptographic operations, it can expose to a number of attacks aimed to break encryption.