Overview
CVE-2025-62626 describes a potential vulnerability in AMD CPUs related to the handling of insufficient entropy when using the RDSEED instruction. This flaw could allow a local attacker to influence the values returned by RDSEED, potentially leading to the consumption of insufficiently random values. The vulnerability was published on 2025-11-21.
Technical Details
The RDSEED instruction is intended to provide random numbers seeded from a hardware random number generator (HRNG). This vulnerability arises from a situation where the hardware RNG doesn’t possess sufficient entropy. If the entropy source is weak or predictable, the output of RDSEED can also become predictable. An attacker with local access could potentially manipulate the system environment in a way that further reduces the entropy available to the HRNG or influences the RDSEED output directly.
Specifically, the core issue lies in the firmware or hardware implementation of the HRNG and the error handling mechanisms associated with insufficient entropy. The specification and implementation may not sufficiently guarantee true randomness in all circumstances, particularly under duress or in virtualized environments.
CVSS Analysis
As reported, CVE-2025-62626 has a CVSS score of N/A and a severity rating of N/A. This suggests that either the risk has not been formally assessed by the reporting entity or is considered to be low impact. The ‘N/A’ may also indicate that this CVE is a placeholder pending a full evaluation of the scope and impact. A low CVSS score doesn’t necessarily imply negligible risk, and further analysis may be required.
Possible Impact
While the official severity is N/A, the potential impact of predictable random numbers should not be underestimated. If an attacker can influence the output of RDSEED, this could have severe consequences for applications relying on the instruction for security-sensitive operations. Examples include:
- Cryptographic Key Generation: Weak random numbers can compromise the security of generated cryptographic keys, allowing attackers to potentially decrypt sensitive data.
- Session ID Generation: Predictable session IDs can allow attackers to hijack user sessions and gain unauthorized access to accounts.
- Security Tokens: Vulnerable token generation could expose systems to authentication bypass attacks.
- Any software relying on true random numbers: This could include gambling software, scientific simulations, and various security applications.
The impact is significantly increased if this weakness is present on a hypervisor, as this could affect multiple virtual machines relying on the same underlying hardware.
Mitigation or Patch Steps
The primary mitigation strategy is to apply any available firmware updates or patches provided by AMD. Check the AMD security bulletin for the specific model and revision of your CPU to see if an update is available.
- Firmware Updates: Install the latest BIOS/UEFI firmware from your motherboard manufacturer. These updates will often include microcode updates from AMD that address security vulnerabilities.
- Operating System Updates: Regularly update your operating system. Operating systems can sometimes provide software-based mitigations or improved entropy gathering techniques.
- Consider Alternative Random Number Sources: For security-critical applications, consider supplementing or replacing RDSEED with other random number sources or libraries that employ techniques to mitigate entropy starvation, such as combining RDSEED with data from other entropy sources (e.g., system interrupts, timers).
