Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-1267 Base Draft
Policy Uses Obsolete Encoding
This vulnerability occurs when a hardware system uses outdated or deprecated encoding methods to enforce security policies and access controls.
Definition
What is CWE-1267?
This vulnerability occurs when a hardware system uses outdated or deprecated encoding methods to enforce security policies and access controls.
In a System-on-a-Chip (SoC), different hardware components constantly generate transactions to read, write, or perform actions like reset or compute. Each transaction includes identifiers for its source and destination, and is often tagged with a Security Token. This token acts as a key, telling the destination what actions the transaction is permitted to perform. A policy encoder is responsible for creating these tokens by mapping transaction details to specific security permissions.
A critical security flaw arises when this policy encoder relies on an obsolete or no-longer-trusted encoding scheme. Using weak or deprecated encoding undermines the entire access control system, as the security tokens can become predictable, forgeable, or easily bypassed. This leaves the chip's assets and functions vulnerable to unauthorized access or manipulation by malicious actors.
Real-world impact
Real-world CVEs caused by CWE-1267
No public CVE references are linked to this CWE in MITRE's catalog yet.
How attackers exploit it
Step-by-step attacker path
- 1
For example, consider a system that has four bus masters. The table below provides bus masters, their Security Tokens, and trust assumptions. | Bus Master | Security Token Decoding | Trust Assumptions | | --- | --- | --- | | Master_0 | "00" | Untrusted | | Master_1 | "01" | Trusted | | Master_2 | "10" | Untrusted | | Master_3 | "11" | Untrusted | The policy encoding is to be defined such that Security Token will be used in implemented access-controls. The bits in the bus transaction that contain Security-Token information are Bus_transaction [15:11]. The assets are the AES-Key registers for encryption or decryption. The key of 128 bits is implemented as a set of four, 32-bit registers. | Register | Field description | | --- | --- | | AES_ENC_DEC_KEY_0 | AES key [0:31] for encryption or decryption, Default 0x00000000 | | AES_ENC_DEC_KEY_1 | AES key [32:63] for encryption or decryption, Default 0x00000000 | | AES_ENC_DEC_KEY_2 | AES key [64:95] for encryption or decryption, Default 0x00000000 | | AES_ENC_DEC_KEY_4 | AES key [96:127] for encryption or decryption, Default 0x00000000 | Below is an example of a policy encoding scheme inherited from a previous project where all "ODD" numbered Security Tokens are trusted.
- 2
The inherited policy encoding is obsolete and does not work for the new system where an untrusted bus master with an odd Security Token exists in the system, i.e., Master_3 whose Security Token is "11". Based on the old policy, the untrusted bus master (Master_3) has access to the AES-Key registers. To resolve this, a register AES_KEY_ACCESS_POLICY can be defined to provide necessary, access controls:
- 3
New Policy: | | | | AES_KEY_ACCESS_POLICY | [31:0] Default 0x00000002 - agent with Security Token "1" has access to AES_ENC_DEC_KEY_0 through AES_ENC_DEC_KEY_4 registers | The AES_KEY_ACCESS_POLICY register defines which agents with a Security Token in the transaction can access the AES-key registers. Each bit in this 32-bit register defines a Security Token. There could be a maximum of 32 security Tokens that are allowed access to the AES-key registers. The number of the bit when set (i.e., "1") allows respective action from an agent whose identity matches the number of the bit and, if "0" (i.e., Clear), disallows the respective action to that corresponding agent. Thus, any bus master with Security Token "01" is allowed access to the AES-Key registers. Below is the Pseudo Code for policy encoding:
Vulnerable code example
Vulnerable code
For example, consider a system that has four bus masters. The table below provides bus masters, their Security Tokens, and trust assumptions. | Bus Master | Security Token Decoding | Trust Assumptions | | --- | --- | --- | | Master_0 | "00" | Untrusted | | Master_1 | "01" | Trusted | | Master_2 | "10" | Untrusted | | Master_3 | "11" | Untrusted | The policy encoding is to be defined such that Security Token will be used in implemented access-controls. The bits in the bus transaction that contain Security-Token information are Bus_transaction [15:11]. The assets are the AES-Key registers for encryption or decryption. The key of 128 bits is implemented as a set of four, 32-bit registers. | Register | Field description | | --- | --- | | AES_ENC_DEC_KEY_0 | AES key [0:31] for encryption or decryption, Default 0x00000000 | | AES_ENC_DEC_KEY_1 | AES key [32:63] for encryption or decryption, Default 0x00000000 | | AES_ENC_DEC_KEY_2 | AES key [64:95] for encryption or decryption, Default 0x00000000 | | AES_ENC_DEC_KEY_4 | AES key [96:127] for encryption or decryption, Default 0x00000000 | Below is an example of a policy encoding scheme inherited from a previous project where all "ODD" numbered Security Tokens are trusted.
If (Bus_transaction[14] == "1")
Trusted = "1"
Else
Trusted = "0"
If (trusted)
Allow access to AES-Key registers
Else
Deny access to AES-Key registers Secure code example
Secure code
New Policy: | | | | AES_KEY_ACCESS_POLICY | [31:0] Default 0x00000002 - agent with Security Token "1" has access to AES_ENC_DEC_KEY_0 through AES_ENC_DEC_KEY_4 registers | The AES_KEY_ACCESS_POLICY register defines which agents with a Security Token in the transaction can access the AES-key registers. Each bit in this 32-bit register defines a Security Token. There could be a maximum of 32 security Tokens that are allowed access to the AES-key registers. The number of the bit when set (i.e., "1") allows respective action from an agent whose identity matches the number of the bit and, if "0" (i.e., Clear), disallows the respective action to that corresponding agent. Thus, any bus master with Security Token "01" is allowed access to the AES-Key registers. Below is the Pseudo Code for policy encoding:
Security_Token[4:0] = Bus_transaction[15:11]
If (AES_KEY_ACCESS_POLICY[Security_Token] == "1")
Allow access to AES-Key registers
Else
Deny access to AES-Key registers 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-1267
- Architecture and Design / Implementation Security Token Decoders should be reviewed for design inconsistency and common weaknesses. Access and programming flows should be tested in both pre-silicon and post-silicon testing.
Detection signals
How to detect CWE-1267
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.
Plexicus auto-detects CWE-1267 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.
Frequently asked questions What is CWE-1267?
How serious is CWE-1267?
What languages or platforms are affected by CWE-1267?
How can I prevent CWE-1267?
How does Plexicus detect and fix CWE-1267?
Where can I learn more about CWE-1267?
Frequently asked questions
What is CWE-1267?
This vulnerability occurs when a hardware system uses outdated or deprecated encoding methods to enforce security policies and access controls.
How serious is CWE-1267?
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-1267?
MITRE lists the following affected platforms: Not OS-Specific, Not Architecture-Specific, Not Technology-Specific.
How can I prevent CWE-1267?
Security Token Decoders should be reviewed for design inconsistency and common weaknesses. Access and programming flows should be tested in both pre-silicon and post-silicon testing.
How does Plexicus detect and fix CWE-1267?
Plexicus's SAST engine matches the data-flow signature for CWE-1267 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-1267?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1267.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-1267
CWE-284 Parent
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CWE-1231 Sibling
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CWE-1233 Sibling
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CWE-1252 Sibling
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CWE-1257 Sibling
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CWE-1259 Sibling
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