Security readout for executives and security teams
Plain-English summary
CVE-2021-26402 is a firmware flaw in AMD Secure Processor handling of BIOS mailbox commands. On affected 2nd and 3rd Gen EPYC platforms, a local low-privileged attacker could corrupt protected areas tied to system management or SEV-ES, risking server integrity and availability.
Executive priority
Treat this as a high-priority firmware hygiene item for AMD EPYC server fleets, especially virtualization infrastructure. It requires local access, but firmware-layer integrity and availability impact can be operationally significant once an attacker has a foothold.
Technical view
The issue is insufficient bounds checking in ASP firmware while processing BIOS mailbox commands. The CVE describes a partially controlled out-of-bounds write to SMM or SEV-ES regions. CVSS 3.1 is 7.1 with local access, low complexity, low privileges, no user interaction, and high integrity and availability impact.
Likely exposure
Exposure is most likely in server fleets using AMD 2nd Gen EPYC or 3rd Gen EPYC systems with affected AGESA/BIOS firmware. Systems using SEV-ES or hosting high-value workloads deserve extra attention because the described target regions are security-sensitive.
Exploitation context
The source bundle does not show CISA KEV listing or cited active exploitation. The CVSS vector requires local access and low privileges, so this is mainly a post-access privilege-boundary and platform-integrity risk, not a remote unauthenticated internet exposure.
Researcher notes
The public bundle identifies CWE-787 and the affected area but does not include exploit details, fixed AGESA versions, or platform-specific BIOS mappings. Validation should rely on AMD-SB-1032 plus OEM firmware matrices, not generic package assumptions.
Mitigation direction
- Review AMD-SB-1032 and OEM advisories for affected platform firmware guidance.
- Inventory 2nd and 3rd Gen EPYC systems and their BIOS or AGESA versions.
- Apply applicable vendor BIOS or firmware updates through normal maintenance controls.
- Prioritize hosts running sensitive virtualization or SEV-ES workloads.
- Limit local shell access to EPYC hosts until firmware status is confirmed.
Validation and detection
- Confirm each EPYC host generation and current BIOS or AGESA version.
- Compare firmware status against AMD-SB-1032 and the hardware vendor advisory.
- Verify patched firmware remains installed after reboot and configuration management cycles.
- Check virtualization hosts using SEV-ES for priority remediation tracking.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-787: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-26402 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H1.85.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.1HighVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://www.amd.com/en/corporate/product-security/bulletin/AMD-SB-1032CVE reference · vendor-advisory
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Out-of-bounds Write
Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.