Security readout for executives and security teams
Plain-English summary
This flaw affects embedded STM32 products that use STMicroelectronics' USB Host Library before 3.5.1. A malicious USB device could trigger a buffer overflow through an endpoint descriptor and potentially run code on the device. Business urgency depends on whether exposed products accept untrusted USB peripherals.
Executive priority
Treat this as a targeted embedded-product risk, not broad enterprise malware exposure. Prioritize products with accessible USB host ports in customer, field, lab, or shared environments. Devices without untrusted USB attachment paths can be handled through normal firmware maintenance.
Technical view
CVE-2021-42553 is a CWE-120 buffer overflow in stm32_mw_usb_host before 3.5.1. The issue occurs when a USB descriptor reports more endpoints than USBH_MAX_NUM_ENDPOINTS. CVSS 3.1 is 6.8 with physical attack vector and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is likely limited to STM32 firmware that integrates the STM32 USB Host Library, commonly with an RTOS such as FreeRTOS, and presents USB host ports to untrusted devices. Software-only services and devices without USB host functionality are not indicated as affected by the provided sources.
Exploitation context
The CVSS vector requires physical access, low complexity, no privileges, and no user interaction. The CVE is not listed as KEV, and the provided sources do not state active exploitation. Practical risk is highest where users can plug arbitrary USB devices into deployed STM32-based equipment.
Researcher notes
Evidence supports a physical-vector buffer overflow tied to USB endpoint descriptor handling. The source bundle names versions before 3.5.1, but downstream STM32Cube package mappings and product-specific firmware adoption are not provided. Validate exposure at source, SBOM, and firmware-build level.
Mitigation direction
- Inventory firmware using stm32_mw_usb_host or STM32Cube USB Host components.
- Upgrade affected integrations to version 3.5.1 or later where applicable.
- Restrict physical access to USB host ports on deployed devices.
- Check STMicroelectronics guidance before shipping patched firmware.
- For maintained forks, confirm descriptor endpoint bounds are enforced.
Validation and detection
- Search source trees and SBOMs for stm32_mw_usb_host usage.
- Confirm the integrated library version is 3.5.1 or later.
- Review USB host descriptor parsing for endpoint-count bounds checks.
- Identify products where untrusted users can attach USB devices.
- Document firmware build lineage for affected STM32 deployments.
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-120: 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-42553 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
- Medium
- CVSS
- 6.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/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:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H0.95.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.8MediumVector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/STMicroelectronics/stm32_mw_usb_host/pull/4CVE reference
- https://github.com/STMicroelectronics/stm32_mw_usb_hostCVE reference
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.
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.