Description

Incorrect boundary conditions in the Layout: Grid component. This vulnerability was fixed in Firefox 155.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.3",
  "pubDate": "2026-09-01T13:20:06.537Z",
  "pubdate": "2026-09-01T13:20:06.537Z",
  "executiveSummary": "A vulnerability exists within the Layout: Grid component of Firefox, stemming from the improper handling of boundary conditions during grid rendering processes.\nThis flaw allows for memory-related irregularities when processing specifically crafted layout structures.\nThe vulnerability affects Firefox versions prior to 155.\nIf successfully exploited, an attacker could potentially induce a crash or trigger unexpected behavior in the rendering engine, leading to memory corruption or out-of-bounds access.\nThe exploitation requires the victim to render malicious content, such as a crafted webpage, which triggers the faulty boundary logic within the browser's CSS grid implementation.\nGiven the nature of rendering engine vulnerabilities, the potential impact includes denial-of-service (DoS) via process termination or, in more severe scenarios, the possibility of arbitrary code execution if memory safety guarantees are sufficiently bypassed.\nThis issue represents a critical risk to browser security, necessitating prompt updates to remediate the underlying logic error within the layout engine.",
  "technicalDetails": "The vulnerability resides within the CSS Grid layout engine of Firefox, specifically concerning the validation and enforcement of geometric boundary conditions. When the browser calculates the positions and dimensions of grid items, it relies on strict mathematical constraints to determine placement within the parent container.\nThe root cause is an incorrect evaluation of these boundaries during the layout reflow or update process. When an attacker provides a crafted layout—typically involving complex grid-template definitions or deeply nested grid items—the internal state of the layout manager can enter an invalid condition.\nSpecifically, the issue occurs when the Layout: Grid component fails to properly sanitize or constrain calculated values, leading to an integer overflow or an out-of-bounds access during the coordinate calculation phase. This error occurs before the browser finalizes the display list, meaning the flaw exists in the core rendering pipeline rather than the hardware acceleration layer.\nThe attack flow begins when a user navigates to a malicious URL containing CSS grid definitions designed to push the boundaries of the rendering engine's internal coordinate system. As the browser parses the document and constructs the CSS Object Model (CSSOM), the engine invokes the vulnerable Grid layout logic. Because the boundary conditions are not correctly enforced, the engine attempts to perform layout calculations that result in improper memory offsets.\nDuring exploitation, the engine may perform read or write operations to memory locations outside the intended buffers allocated for the grid structure. If the browser attempts to access or store data based on these corrupted boundary values, it may trigger an access violation, causing the content process to crash. In more sophisticated attack scenarios, an attacker could potentially leverage this memory corruption to overwrite adjacent data structures, potentially influencing the browser's execution flow if further primitives are chained.\nThe component responsible for this failure is strictly isolated to the browser's CSS rendering subsystem. No specific authentication or elevated privileges are required for exploitation, as the vulnerability is triggered through standard browser functionality (page rendering). The issue was identified and patched in Firefox 155, effectively hardening the boundary validation logic to ensure that coordinate calculations remain within safe, predefined limits regardless of the input CSS structures."
}