CVE-2015-2713 in Firefox
Summary
by MITRE
Use-after-free vulnerability in the SetBreaks function in Mozilla Firefox before 38.0, Firefox ESR 31.x before 31.7, and Thunderbird before 31.7 allows remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption) via a document containing crafted text in conjunction with a Cascading Style Sheets (CSS) token sequence containing properties related to vertical text.
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Analysis
by VulDB Data Team • 10/22/2024
The CVE-2015-2713 vulnerability represents a critical use-after-free flaw in Mozilla Firefox and Thunderbird browsers that emerged from improper memory management during CSS processing. This vulnerability specifically affects the SetBreaks function within the browser's rendering engine, where memory allocated for document text processing becomes accessible after being freed, creating a dangerous condition that adversaries can exploit. The flaw manifests when browsers encounter specially crafted HTML documents containing text elements combined with specific CSS token sequences that manipulate vertical text properties. This particular combination triggers a memory corruption scenario that can be leveraged by remote attackers to execute arbitrary code on affected systems or cause intentional denial of service conditions.
The technical exploitation of this vulnerability stems from the browser's handling of CSS properties related to vertical text rendering, particularly when processing documents that contain both complex text content and specific CSS directives. When the SetBreaks function processes these crafted inputs, it fails to properly validate memory references, leading to a situation where freed heap memory can be accessed and manipulated by malicious code. This use-after-free condition creates a predictable memory corruption pattern that allows attackers to overwrite critical memory locations, potentially enabling code execution at kernel or user privileges depending on the target system configuration. The vulnerability's exploitation requires a sophisticated attack vector involving precise document construction that combines HTML text elements with CSS properties that trigger the specific memory management flaw.
From an operational impact perspective, this vulnerability poses significant risks to organizations relying on affected browser versions, as it enables remote code execution without requiring user interaction beyond visiting a malicious webpage. The heap memory corruption can lead to unpredictable system behavior, application crashes, or complete system compromise depending on the exploitation success. Security researchers have classified this vulnerability as highly dangerous due to its remote exploitability and the potential for privilege escalation, particularly when users browse untrusted websites or open malicious documents. The affected versions include Firefox 38.0 and earlier, Firefox ESR 31.x versions prior to 31.7, and Thunderbird versions before 31.7, making it a widespread concern across multiple Mozilla products.
Organizations should prioritize immediate patch deployment to address this vulnerability, as the window for exploitation remains open for systems running vulnerable versions. The recommended mitigation involves updating to Firefox 38.0 or later, Firefox ESR 31.7 or later, and Thunderbird 31.7 or later, which contain the necessary memory management fixes. Security teams should implement network-based protections including web application firewalls and content filtering systems to block access to known malicious domains that may host exploit code. Additionally, browser hardening measures such as disabling unnecessary CSS features and implementing strict content security policies can reduce the attack surface. This vulnerability aligns with CWE-416, which describes the use of freed memory condition, and represents a typical example of memory safety issues that fall under ATT&CK technique T1059 for execution through command and scripting interpreters, demonstrating how browser-based vulnerabilities can enable broader attack chains.
The remediation process requires comprehensive testing of patched versions to ensure compatibility with existing applications and services while maintaining security posture. Organizations should conduct thorough vulnerability assessments to identify any systems still running vulnerable versions and establish automated patch management processes to prevent future exposure. Regular security monitoring and incident response procedures should be enhanced to detect potential exploitation attempts, as the vulnerability's exploitation pattern may be detected through anomalous memory access patterns or unexpected application behavior. Security professionals should also consider implementing browser sandboxing and privilege separation mechanisms to limit the potential impact if exploitation occurs despite preventive measures.