Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
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
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Missing protection mechanism on serial connection allows for arbitrary OS command execution.
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Mini-PCI Express slot does not restrict direct memory access.
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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).
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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.
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monitor device allows access to physical UART debug port without authentication
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 4
Iterate until the response leaks data, executes attacker code, or escalates privileges.
Vulnerable code example
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.
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
Run dynamic application security testing against the live endpoint.
Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.
Code review: flag any new code that handles input from this surface without using the validated framework helpers.
CWE-1299
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Frequently asked questions What is CWE-1299?
How serious is CWE-1299?
What languages or platforms are affected by CWE-1299?
How can I prevent CWE-1299?
How does Plexicus detect and fix CWE-1299?
Where can I learn more about CWE-1299?
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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