CWE-1021: Improper Restriction of Rendered UI Layers or Frames

BaseIncomplete

The web application does not restrict or incorrectly restricts frame objects or UI layers that belong to another application or domain.

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Technical Details

Structure
Simple
Vulnerability Mapping
ALLOWED

Applicable To

Languages
Not Language-Specific
Platforms

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-1021 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-1021, Improper Restriction of Rendered UI Layers or Frames, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Improper Restriction of Rendered UI Layers or Frames during Implementation

MITRE associates mitigation with Implementation; documented detection approaches include Automated Static Analysis; recorded impacts include Gain Privileges or Assume Identity, Bypass Protection Mechanism, Read Application Data, and Modify Application Data. Use these source-defined anchors to turn CWE-1021 into implementation, review, and verification checks for the affected component.

CWE-1021: Improper Restriction of Rendered UI Layers or Frames — MITRE CWE

Triage CWE-1021 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-1021, Improper Restriction of Rendered UI Layers or Frames, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-1021

Apply MITRE's full root-cause mapping guidance when using CWE-1021, Improper Restriction of Rendered UI Layers or Frames. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-1021 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-1021, Improper Restriction of Rendered UI Layers or Frames. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-1021: Improper Restriction of Rendered UI Layers or Frames?+

CWE-1021: Improper Restriction of Rendered UI Layers or Frames is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The web application does not restrict or incorrectly restricts frame objects or UI layers that belong to another application or domain.

What are the security consequences of Improper Restriction of Rendered UI Layers or Frames?+

If exploited, CWE-1021 (Improper Restriction of Rendered UI Layers or Frames) it can compromise Access Control, leading to outcomes such as Gain Privileges or Assume Identity, Bypass Protection Mechanism, Read Application Data and Modify Application Data.

How do you prevent or mitigate Improper Restriction of Rendered UI Layers or Frames?+

Recommended mitigations for CWE-1021 include: The use of X-Frame-Options allows developers of web content to restrict the usage of their application within the form of overlays, frames, or iFrames. The developer can indicate from which domains can frame the content. The concept of X-Frame-Options is well documented, but implementation of this protection mechanism is in development to cover gaps. There is a need for allowing frames from multiple domains. A developer can use a "frame-breaker" script in each page that should not be framed. This is very helpful for legacy browsers that do not support X-Frame-Options security feature previously mentioned. It is also important to note that this tactic has been circumvented or bypassed. Improper usage of frames can persist in the web application through nested frames. The "frame-breaking" script does not intuitively account for multiple nested frames that can be presented to the user. This defense-in-depth technique can be used to prevent the improper usage of frames in web applications. It prioritizes the valid sources of data to be loaded into the application through the usage of declarative policies. Based on which implementation of Content Security Policy is in use, the developer should use the "frame-ancestors" directive or the "frame-src" directive to mitigate this weakness. Both directives allow for the placement of restrictions when it comes to allowing embedded content.

Which programming languages are affected by Improper Restriction of Rendered UI Layers or Frames?+

CWE-1021 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What are real-world examples of Improper Restriction of Rendered UI Layers or Frames?+

MITRE documents real CVEs mapped to CWE-1021, including CVE-2017-7440, CVE-2017-5697, CVE-2017-4015, CVE-2016-2496 and CVE-2015-1241. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-1021 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

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