CWE-1223 Base Incomplete

Race Condition for Write-Once Attributes

This vulnerability occurs when an untrusted software component wins a race condition and writes to a hardware register before the trusted component can, permanently locking in an insecure value…

Definition

What is CWE-1223?

This vulnerability occurs when an untrusted software component wins a race condition and writes to a hardware register before the trusted component can, permanently locking in an insecure value because the register is designed to be written only once.
In hardware design, critical security settings are often stored in write-once registers. These registers allow software to set a value—like a system configuration or a security policy—a single time after a reset, after which they become read-only. This mechanism is intended to let trusted boot firmware establish a secure baseline that untrusted runtime software cannot later alter. A security flaw emerges when the hardware design does not properly sequence access to these registers. If an untrusted software module (Module B) can issue a write command before the trusted module (Module A) does, the untrusted value gets permanently locked in. The trusted module's subsequent write is ignored, leaving the system configured with potentially insecure or incorrect settings for its entire operational lifetime.
Real-world impact

Real-world CVEs caused by CWE-1223

No public CVE references are linked to this CWE in MITRE's catalog yet.

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

consider the example design module system verilog code shown below. register_write_once_example module is an example of register that has a write-once field defined. Bit 0 field captures the write_once_status value.

Vulnerable Verilog 
module register_write_once_example
 (

```
   input [15:0] Data_in,
   input Clk,
   input ip_resetn,
   input global_resetn,
   input write,
   output reg [15:0] Data_out
 );
 reg Write_once_status;
 always @(posedge Clk or negedge ip_resetn)
 if (~ip_resetn)
   begin
  	 Data_out <= 16'h0000; 
  	 Write_once_status <= 1'b0;
   end
 else if (write & ~Write_once_status) 
   begin
  	 Data_out <= Data_in & 16'hFFFE; // Input data written to register after masking bit 0
  	 Write_once_status <= 1'b1; // Write once status set after first write.
   end
 else if (~write)
   begin
  	 Data_out[15:1] <= Data_out[15:1];
  	 Data_out[0] <= Write_once_status;
   end
 endmodule
Secure code example

Secure Other

The first system component that sends a write cycle to this register can program the value. This could result in a race condition security issue in the SoC design, if an untrusted agent is running in the system in parallel with the trusted component that is expected to program the register.

Secure Other 
Trusted firmware or software trying to set the write-once field: 

  - Must confirm the Write_once_status (bit 0) value is zero, before programming register. If another agent has programmed the register before, then Write_once_status value will be one.

  - After writing to the register, the trusted software can issue a read to confirm that the valid setting has been programmed.
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-1223

  • Architecture and Design During hardware design all register write-once or sticky fields must be evaluated for proper configuration.
  • Testing The testing phase should use automated tools to test that values are not reprogrammable and that write-once fields lock on writing zeros.
Detection signals

How to detect CWE-1223

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-1223 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-1223?

This vulnerability occurs when an untrusted software component wins a race condition and writes to a hardware register before the trusted component can, permanently locking in an insecure value because the register is designed to be written only once.

How serious is CWE-1223?

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-1223?

MITRE lists the following affected platforms: Verilog, VHDL, System on Chip.

How can I prevent CWE-1223?

During hardware design all register write-once or sticky fields must be evaluated for proper configuration. The testing phase should use automated tools to test that values are not reprogrammable and that write-once fields lock on writing zeros.

How does Plexicus detect and fix CWE-1223?

Plexicus's SAST engine matches the data-flow signature for CWE-1223 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-1223?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1223.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-1223

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Resources

Further reading

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