CWE-1299 Base Draft

Missing Protection Mechanism for Alternate Hardware Interface

This vulnerability occurs when a hardware component's security controls only protect the primary access path, leaving alternate interfaces unprotected. Attackers can bypass intended restrictions by…

Definition

What is CWE-1299?

This vulnerability occurs when a hardware component's security controls only protect the primary access path, leaving alternate interfaces unprotected. Attackers can bypass intended restrictions by accessing sensitive assets through these unguarded backdoors, such as shadow registers or other external-facing ports.
Modern chips and Systems-on-Chip (SoCs) often contain multiple access paths to critical internal registers—through interfaces like PCIe, USB, UART, or SMBus. If access controls are only enforced on one primary interface (e.g., PCIe), an attacker can simply route malicious transactions through an alternate, unprotected interface (like UART or USB) to modify or read protected registers, completely bypassing the intended security layer. Another common bypass involves shadow or mirror registers, which are duplicate registers that temporarily hold data before syncing with a main register. These are often implemented for performance or debugging purposes. If these shadow registers lack the same access protections as their primary counterparts, attackers can directly target them to alter system state, compromise security configurations, or leak sensitive information, effectively undermining the chip's entire protection scheme.
Real-world impact

Real-world CVEs caused by CWE-1299

  • CVE-2022-38399

    Missing protection mechanism on serial connection allows for arbitrary OS command execution.

  • CVE-2020-9285

    Mini-PCI Express slot does not restrict direct memory access.

  • CVE-2020-8004

    When the internal flash is protected by blocking access on the Data Bus (DBUS), it can still be indirectly accessed through the Instruction Bus (IBUS).

  • CVE-2017-18293

    When GPIO is protected by blocking access to corresponding GPIO resource registers, protection can be bypassed by writing to the corresponding banked GPIO registers instead.

  • CVE-2020-15483

    monitor device allows access to physical UART debug port without authentication

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable Verilog

Vulnerable Verilog 
assign addr_auth = (address == 32'hF00) ? 1: 0;
Secure code example

Secure Verilog

The bugged line of code is repeated in the Bad example above. The weakness arises from the fact that the SECURE_ME register can be modified by writing to the shadow register COPY_OF_SECURE_ME. The address of COPY_OF_SECURE_ME should also be included in the check. That buggy line of code should instead be replaced as shown in the Good Code Snippet below.

Secure Verilog 
assign addr_auth = (address == 32'hF00 || address == 32'h800F00) ? 1: 0;
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-1299

  • Requirements Protect assets from accesses against all potential interfaces and alternate paths.
  • Architecture and Design Protect assets from accesses against all potential interfaces and alternate paths.
  • Implementation Protect assets from accesses against all potential interfaces and alternate paths.
Detection signals

How to detect CWE-1299

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-1299 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-1299?

This vulnerability occurs when a hardware component's security controls only protect the primary access path, leaving alternate interfaces unprotected. Attackers can bypass intended restrictions by accessing sensitive assets through these unguarded backdoors, such as shadow registers or other external-facing ports.

How serious is CWE-1299?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-1299?

MITRE lists the following affected platforms: Not OS-Specific, Not Architecture-Specific, Microcontroller Hardware, Processor Hardware, Bus/Interface Hardware, Not Technology-Specific.

How can I prevent CWE-1299?

Protect assets from accesses against all potential interfaces and alternate paths. Protect assets from accesses against all potential interfaces and alternate paths.

How does Plexicus detect and fix CWE-1299?

Plexicus's SAST engine matches the data-flow signature for CWE-1299 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-1299?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1299.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-1299

CWE-420 Parent

Unprotected Alternate Channel

This vulnerability occurs when an application secures its main communication path but leaves a backup or alternative channel with weaker…

CWE-421 Sibling

Race Condition During Access to Alternate Channel

A race condition occurs when an application opens a secondary communication channel intended for an authorized user, but fails to secure…

CWE-422 Sibling

Unprotected Windows Messaging Channel ('Shatter')

This vulnerability, often called a 'Shatter' attack, occurs when a Windows application running with high privileges accepts messages from…

CWE-1191 Peer

On-Chip Debug and Test Interface With Improper Access Control

This vulnerability occurs when a hardware chip's debug or test interface (like JTAG) lacks proper access controls. Without correct…

Resources

Further reading

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