Firefox: Improper Restriction of Rendered UI Layers or Frames
CVE-2025-1940 is a high-severity improper restriction of rendered UI layers or frames vulnerability in Firefox from Mozilla, with a CVSS 3.1 base score of 7.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. There is no confirmed exploitation so far. EPSS estimates a 0.25% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of Firefox you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on mozilla.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- LowLimited modification of data is possible.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N. Scored by CISA (ADP).
Official description
A select option could partially obscure the confirmation prompt shown before launching external apps. This could be used to trick a user in to launching an external app unexpectedly. *This issue only affects Android versions of Firefox.*. This vulnerability was fixed in Firefox 136.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Restriction of Rendered UI Layers or Frames
The web application does not restrict or incorrectly restricts frame objects or UI layers that belong to another application or domain.
How developers prevent this class of flaw
- Use the frame-ancestors directive in the Content Security Policy, which is intended to define restrictions when it comes to allowing embedded content.
- The use of X-Frame-Options (now partially obsolete as of September 2026) 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; often, there is a need for allowing frames from multiple domains.
- Use a frame-breaker script in each page that should not be framed. This is very helpful for legacy browsers that do not support the X-Frame-Options security feature previously mentioned (which is now partially obsolete).
More Improper Restriction of Rendered UI Layers or Frames vulnerabilities (CWE-1021)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Other references
- bugzilla.mozilla.org/show_bug.cgi?id=1908488Issue Tracking
Other vulnerabilities in Firefox
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
Recent Improper Restriction of Rendered UI Layers or Frames vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.1 High severity
- 7.5 High severity
- 7.5 High severity
- 8.1 High severity
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