CyberSecBulletin
CVE-2023-20520NVD status: Modified

1st Gen AMD EPYC™: Out-of-bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2023-20520 is a critical-severity out-of-bounds write vulnerability in 1st Gen AMD EPYC™ from AMD, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected 1st Gen AMD EPYC™ versions: various. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.79% chance of exploitation within 30 days, higher than 57% of scored CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Check which version of 1st Gen AMD EPYC™ you run against the affected versions below, and install the vendor's latest release.
  2. Read the advisory on amd.com for workarounds and exact fixed builds.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
AMD1st Gen AMD EPYC™variousNot stated
AMD2nd Gen AMD EPYC™variousNot stated
AMD3rd Gen AMD EPYC™variousNot stated
AMDEpyc 72f3 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7313 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7313p Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7343 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7373x Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 73f3 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7413 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7443 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7443p Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7453 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7473x Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 74f3 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7513 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7543 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7543p Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7573x Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 75f3 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7643 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7663 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7713 Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7713p Firmwaremilanpi_1.0.0.5Not stated
AMDEpyc 7763 Firmwaremilanpi_1.0.0.5Not stated

Version data comes from the organisation that assigned the CVE; 35 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.19.8CriticalNVD
CVSS 3.19.8CriticalCISA (ADP)

Official description

Improper access control settings in ASP Bootloader may allow an attacker to corrupt the return address causing a stack-based buffer overrun potentially leading to arbitrary code execution.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
  • Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.

More Out-of-bounds Write vulnerabilities (CWE-787)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Write vulnerabilities

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