PolarSSL versions prior to v1.1 use the HAVEGE random number generation algorithm. At its heart, this uses timing information based on the processor's high resolution timer (the RDTSC instruction). This instruction can be virtualized, and some virtual machine hosts have chosen to disable this instruction, returning 0s or predictable results.

References

• https://nvd.nist.gov/vuln/detail/CVE-2011-4574
• https://tls.mbed.org/tech-updates/security-advisories/polarssl-security-advisory-2011-02