Full Report
Learn about the impact in cloud environments of CVE-2023-20593, a cross-process information leak vulnerability in AMD Zen 2 Processors.
Analysis Summary
# Vulnerability: Zenbleed Data Leakage via Speculative Execution Flaw in AMD Zen 2 CPUs
## CVE Details
- CVE ID: CVE-2023-20593
- CVSS Score: N/A (Severity is assessed contextually in the report, often high for hardware vulnerabilities leading to data leaks, but described as **low severity in cloud environments** due to required local execution)
- CWE: Improper handling of instruction execution (Likely related to improper input validation during speculative execution, leading to misuse of the `vzeroupper` instruction)
## Affected Systems
- Products: AMD CPUs using the Zen 2 architecture
- Versions: All CPUs built on the Zen 2 architecture, specifically:
- Ryzen 3000 ("Matisse")
- Ryzen 4000U/H ("Renoir")
- Ryzen 5000U ("Lucienne")
- Ryzen 7020
- ThreadRipper 3000
- Epyc server ("Rome")
- Configurations: Affects all operating systems. Exploitation requires local code execution on the host system.
## Vulnerability Description
CVE-2023-20593 is a use-after-free (or similar logic flaw) vulnerability triggered by improper handling of the `vzeroupper` instruction during speculative execution on AMD Zen 2 processors. This flaw allows an unprivileged local attacker to reliably read sensitive data (passwords, encryption keys) from privileged processes, isolated sandboxes, virtual machines, and containers. The attack leverages "Oracle Serialization" techniques to verify the data leakage triggered by the speculative execution path.
## Exploitation
- Status: Vendor patches available, but this is a critical hardware flaw verified by researchers.
- Complexity: Low prerequisites once local code execution is achieved. The attack itself is reliable and immediate.
- Attack Vector: Local (Requires an attacker to already have code execution on the target machine).
## Impact
- Confidentiality: High (Allows leakage of sensitive data from privileged operational memory).
- Integrity: Low (Read-only vulnerability).
- Availability: Low (Minimal impact on system availability).
## Remediation
### Patches
- The fix is implemented via **AMD microcode updates**.
- Users must obtain the microcode update through a **future BIOS/firmware upgrade** from their computer or server vendor.
- Cloud providers (CSPs) apply this fix at the host level.
### Workarounds
- **In Cloud/VM Environments:** No effective workarounds are available to customers within a VM, as the patch must be applied by the host CSP. Customers using affected instance types (excluding GCP customers who confirmed patching) should ensure all other security controls are robust until CSPs confirm microcode application.
- **Hardware Mitigation:** The mentioned "chicken bit" mitigation is not accessible to VM customers.
## Detection
- **Indicators of Compromise:** The research does not detail specific IoCs outside of successful exploitation resulting in unexpected data copies.
- **Detection Methods and Tools:**
- **Host Check (Linux):** Check CPU microcode version against the patched version (e.g., 0x0830107A as of publication) using:
bash
$ grep 'microcode' /proc/cpuinfo
- **Host Check (Linux):** Verify CPU model name using `lscpu` to see if it belongs to the Zen 2 family.
- Security platforms (e.g., Wiz Threat Center) may offer pre-built queries to identify affected instances based on kernel/package information, although this does not confirm host patching.
## References
- Tavis Ormandy blog: hxxps://lock.cmpxchg8b.com/zenbleed.html#vulnerability
- AMD’s advisory: hxxps://www.amd.com/en/resources/product-security/bulletin/amd-sb-7008.html
- GCP's bulletin: hxxps://cloud.google.com/support/bulletins#gcp-2023-020
- AWS's advisory: hxxps://aws.amazon.com/security/security-bulletins/AWS-2023-004/