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Weakness · BaseCWE-1021

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

Base

As of 2026-10-10, CWE-1021 (Improper Restriction of Rendered UI Layers or Frames) underlies 4 CVEs tracked by Threadlinqs, none of them in the CISA Known Exploited Vulnerabilities catalog, and is cited by 70 tracked threats.

CVEs
4Mapped to CWE-1021
CISA KEV
0None listed yet
Critical
0CVSS v3 critical CVEs
Threats
70Tracked campaigns citing it
Likelihood
—MITRE likelihood of exploit

Last updated:

What is CWE-1021?

The web application does not restrict or incorrectly restricts frame objects or UI layers that belong to another application or domain, which can lead to user confusion about which interface the user is interacting with.

A web application is expected to place restrictions on whether it is allowed to be rendered within frames, iframes, objects, embed or applet elements. Without the restrictions, users can be tricked into interacting with the application when they were not intending to.

CWE-1021 is a base-level weakness in MITRE’s Common Weakness Enumeration. Applicable platforms: Language: Not Language-Specific; Technology: Not Technology-Specific; Technology: Web Based.

Source: MITRE CWE (CWE-1021 definition, reproduced verbatim). Counts and linkage below are Threadlinqs data.

Consequences

  • Access Control — Gain Privileges or Assume Identity, Bypass Protection Mechanism, Read Application Data, Modify Application Data. An attacker can trick a user into performing actions that are masked and hidden from the user's view. The impact varies widely, depending on the functionality of the underlying application. For example, in a social media application, clickjacking could be used to trik the user into changing privacy settings.

Source: MITRE CWE, common consequences.

How CWE-1021 is exploited in the wild

Threadlinqs maps 4 CVEs to CWE-1021, published between 2026-06-16 and 2026-09-09. None of them is in the CISA KEV catalog yet. By CVSS v3 severity the set splits into 1 high, 3 medium. The highest EPSS score in the set is 0.3% (CVE-2026-60370), the modelled probability of exploitation in the next 30 days. 70 tracked threats reference CWE-1021 directly or through a CVE it covers; the most recent is “Fake ChatGPT/Gemini/Claude Ad-Tool Lure Sites Use Browser-in-the-Browser Phishing to Steal Ad Account Credentials and MFA Codes” (2026-10-06). Affected products concentrate in Mozilla (2), Google (1), Oracle Corporation (1).

Vulnerabilities (CVEs)

All 4 CVEs mapped to CWE-1021, CISA KEV first, then by CVSS score.

  • CVE-2026-60370 — CVSS 7.5 high · EPSS 0.3% · published 2026-07-22
  • CVE-2026-12322 — CVSS 5.4 medium · EPSS 0.2% · published 2026-06-16
  • CVE-2026-12323 — CVSS 5.4 medium · EPSS 0.1% · published 2026-06-16
  • CVE-2026-87486 — CVSS 4 medium · EPSS 0.1% · published 2026-09-09

Affected vendors

Threat activity

70 tracked threats cite CWE-1021; the 25 most recent are listed.

Mitigations

  • Implementation: 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.
  • Implementation: 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.
  • Implementation: 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.

Source: MITRE CWE, potential mitigations.

Detection methods (MITRE CWE)

  • Automated Static Analysis (effectiveness: High): Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Source: MITRE CWE, detection methods. Threadlinqs detection rules for the threats above are Blue tier and higher.