CVE-2026-7328 Overview
CVE-2026-7328 is a missing authorization vulnerability [CWE-862] in Caliptra Core Runtime Firmware version 2.1.0 operating in subsystem mode. The flaw affects three mailbox commands: INVOKE_DPE_MLDSA87, CM_AES_GCM_DECRYPT_DMA, and EXTERNAL_MAILBOX_CMD. These commands accept AXI (Advanced eXtensible Interface) addresses without proper verification. A privileged local attacker can submit crafted mailbox commands referencing unverified AXI addresses to trigger a denial of service condition on the Caliptra root-of-trust silicon component.
Critical Impact
A privileged local attacker can disrupt availability of the Caliptra root-of-trust firmware through malformed mailbox commands. Secondary integrity impact depends on the integrating platform.
Affected Products
- Caliptra Core Runtime Firmware 2.1.0
- Systems operating Caliptra in subsystem mode
- Silicon platforms integrating Caliptra as a root-of-trust component
Discovery Timeline
- 2026-07-22 - CVE CVE-2026-7328 published to NVD
- 2026-07-22 - Last updated in NVD database
Technical Details for CVE-2026-7328
Vulnerability Analysis
Caliptra is an open-source silicon root-of-trust developed under the CHIPS Alliance. Its Core Runtime Firmware exposes a mailbox interface that hosts and subsystem components use to submit commands. Three commands — INVOKE_DPE_MLDSA87, CM_AES_GCM_DECRYPT_DMA, and EXTERNAL_MAILBOX_CMD — accept AXI addresses as parameters. The firmware fails to validate that these addresses fall within permissible memory regions before dereferencing them for DMA (Direct Memory Access) operations.
When the firmware operates in subsystem mode, this missing authorization allows an attacker with local privileged access to pass arbitrary AXI addresses. The runtime then attempts operations against unverified memory regions, causing execution to fault or the firmware to enter an unrecoverable state. This disrupts availability of the root-of-trust services relied upon by higher-level components.
Root Cause
The root cause is a missing authorization check on AXI address parameters passed through the mailbox interface. The affected commands trust caller-supplied addresses without validating them against an allowlist or expected address range. This violates the principle of complete mediation required for security-critical firmware handling arbitrary DMA targets.
Attack Vector
Exploitation requires local access with existing privileges on the platform hosting Caliptra. The attacker submits a mailbox command with an AXI address pointing to a region that Caliptra should not access. Because the command handlers omit authorization checks, the firmware acts on the address and enters an error state. Confidentiality and integrity impact within Caliptra itself is none, but availability is high. Downstream integrity effects depend on how the integrator uses the responses.
Refer to the GitHub Security Advisory GHSA-c5v4-q445-wv84 for command-level technical details.
Detection Methods for CVE-2026-7328
Indicators of Compromise
- Unexpected Caliptra firmware resets, hangs, or fault states observed through platform telemetry.
- Mailbox command traces containing INVOKE_DPE_MLDSA87, CM_AES_GCM_DECRYPT_DMA, or EXTERNAL_MAILBOX_CMD with AXI addresses outside expected ranges.
- Repeated failed mailbox responses correlating with subsequent root-of-trust unavailability.
Detection Strategies
- Instrument the mailbox transport layer to log source, command opcode, and AXI address parameters for the three affected commands.
- Build baseline profiles of legitimate AXI address ranges used by trusted subsystem callers and alert on deviations.
- Correlate Caliptra reset events with preceding mailbox command sequences to identify triggering commands.
Monitoring Recommendations
- Forward Caliptra health telemetry and mailbox audit logs to a central SIEM for retention and correlation.
- Monitor platform management controllers for abnormal frequency of root-of-trust restarts.
- Track which local principals invoke privileged mailbox commands and alert on unauthorized callers.
How to Mitigate CVE-2026-7328
Immediate Actions Required
- Inventory silicon and platform firmware to identify any deployment of Caliptra Core Runtime Firmware 2.1.0 in subsystem mode.
- Restrict local privileged access to systems exposing the Caliptra mailbox interface to only trusted administrators and services.
- Apply the vendor-supplied firmware update once released by the CHIPS Alliance Caliptra project.
Patch Information
Consult the Caliptra GitHub Security Advisory GHSA-c5v4-q445-wv84 for the fixed firmware version and integration guidance. Platform integrators must rebuild and re-sign firmware images incorporating the patched Core Runtime Firmware before flashing to affected silicon.
Workarounds
- Disable or filter the INVOKE_DPE_MLDSA87, CM_AES_GCM_DECRYPT_DMA, and EXTERNAL_MAILBOX_CMD commands at the mailbox transport if operationally feasible.
- Enforce strict access controls on host-side interfaces that can reach the Caliptra mailbox to reduce the pool of privileged local callers.
- Validate AXI address parameters at an upstream policy layer before forwarding commands to Caliptra when firmware patching is delayed.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
