CVE-2016-5271 in Firefox
Summary
by MITRE
The PropertyProvider::GetSpacingInternal function in Mozilla Firefox before 49.0 allows remote attackers to cause a denial of service (out-of-bounds read and application crash) via text runs in conjunction with a "display: contents" Cascading Style Sheets (CSS) property.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-5271 represents a critical out-of-bounds read flaw within Mozilla Firefox's rendering engine that affects versions prior to 49.0. This vulnerability specifically resides in the PropertyProvider::GetSpacingInternal function, which processes CSS styling properties during page rendering. The flaw manifests when Firefox encounters text runs combined with the CSS "display: contents" property, creating a scenario where memory access occurs beyond the bounds of allocated buffers. Such out-of-bounds reads typically arise from inadequate input validation and boundary checking within the browser's CSS processing pipeline, allowing malicious actors to exploit the vulnerability through carefully crafted web content.
The technical exploitation of this vulnerability occurs through a combination of CSS properties that create an unexpected execution path within Firefox's layout engine. When the browser processes elements with display: contents, it attempts to calculate spacing and positioning values, but the PropertyProvider::GetSpacingInternal function fails to properly validate array indices or buffer boundaries during these calculations. This allows attackers to craft malicious CSS that triggers memory access violations, resulting in application crashes and potential denial of service conditions. The vulnerability falls under the CWE-129 weakness category, which encompasses issues related to improper validation of array indices and buffer overflows, and aligns with ATT&CK technique T1203 for process injection and T1499 for network denial of service through application-level attacks.
The operational impact of CVE-2016-5271 extends beyond simple application instability, as it provides attackers with a reliable method for causing persistent denial of service against Firefox users. Remote attackers can construct web pages containing malicious CSS combinations that will trigger the vulnerability whenever users navigate to those pages, effectively creating a vector for distributed denial of service attacks. The flaw's exploitation does not require user interaction beyond visiting a compromised website, making it particularly dangerous in phishing campaigns or malicious advertising networks. Additionally, the vulnerability's potential for escalation exists in environments where Firefox is used as a component in larger applications, as the crash conditions could be leveraged to disrupt service availability or potentially serve as a stepping stone for more sophisticated attacks. Organizations relying on Firefox for web browsing must implement immediate patch management protocols to address this vulnerability, as the out-of-bounds read conditions can be reliably triggered through standard web browsing activities without requiring special privileges or complex attack vectors.