CWE-1303 Base Draft

Non-Transparent Sharing of Microarchitectural Resources

This vulnerability occurs when a processor's internal performance features, like caches and branch predictors, are unintentionally shared between different software contexts. This breaks the…

Definition

What is CWE-1303?

This vulnerability occurs when a processor's internal performance features, like caches and branch predictors, are unintentionally shared between different software contexts. This breaks the expected isolation, allowing data to leak across security boundaries.
Modern CPUs use performance-boosting techniques like out-of-order execution, speculation, and caching. The problem is that the hardware implementation of these features often shares physical resources between apps, virtual machines, or security domains in ways not documented in the architecture. Since this sharing is invisible to software, it creates hidden communication channels that malicious programs can exploit to steal sensitive information from other contexts. Attackers have leveraged shared resources like CPU caches, branch prediction buffers, and load-store queues to build these covert channels. Speculative execution further amplifies the risk by giving attackers more precise control over what data gets leaked. Without clear documentation on how these microarchitectural resources are shared, it's nearly impossible for developers and system designers to guarantee protection against such side-channel attacks.
Real-world impact

Real-world CVEs caused by CWE-1303

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 pseudo

MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
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-1303

  • Architecture and Design Microarchitectural covert channels can be addressed using a mixture of hardware and software mitigation techniques. These include partitioned caches, new barrier and flush instructions, and disabling high resolution performance counters and timers.
  • Requirements Microarchitectural covert channels can be addressed using a mixture of hardware and software mitigation techniques. These include partitioned caches, new barrier and flush instructions, and disabling high resolution performance counters and timers.
Detection signals

How to detect CWE-1303

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-1303 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-1303?

This vulnerability occurs when a processor's internal performance features, like caches and branch predictors, are unintentionally shared between different software contexts. This breaks the expected isolation, allowing data to leak across security boundaries.

How serious is CWE-1303?

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-1303?

MITRE lists the following affected platforms: Not OS-Specific, Not Architecture-Specific, Not Technology-Specific.

How can I prevent CWE-1303?

Microarchitectural covert channels can be addressed using a mixture of hardware and software mitigation techniques. These include partitioned caches, new barrier and flush instructions, and disabling high resolution performance counters and timers. Microarchitectural covert channels can be addressed using a mixture of hardware and software mitigation techniques. These include partitioned caches, new barrier and flush instructions, and disabling high resolution performance counters and timers.

How does Plexicus detect and fix CWE-1303?

Plexicus's SAST engine matches the data-flow signature for CWE-1303 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-1303?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1303.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-1303

CWE-1189 Parent

Improper Isolation of Shared Resources on System-on-a-Chip (SoC)

This vulnerability occurs when a System-on-a-Chip (SoC) fails to properly separate shared hardware resources between secure (trusted) and…

Resources

Further reading

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