CVE-2015-0823 in Firefox
Summary
by MITRE
Multiple use-after-free vulnerabilities in OpenType Sanitiser, as used in Mozilla Firefox before 36.0, might allow remote attackers to trigger problematic Developer Console information or possibly have unspecified other impact by leveraging incorrect macro expansion, related to the ots::ots_gasp_parse function.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 03/10/2022
The vulnerability identified as CVE-2015-0823 represents a critical use-after-free flaw within the OpenType Sanitiser component of Mozilla Firefox versions prior to 36.0. This security issue resides in the ots::ots_gasp_parse function which processes OpenType font files, specifically targeting the gasp table that controls grid-fitting behavior for font rendering. The flaw stems from improper memory management during the parsing of font data structures, creating conditions where freed memory locations could be accessed again by subsequent operations. This vulnerability demonstrates a classic memory safety issue that has significant implications for browser security and user protection.
The technical exploitation of this vulnerability occurs through malformed OpenType font files that trigger incorrect macro expansion within the sanitiser's parsing logic. When Firefox processes these specially crafted font files, the ots_gasp_parse function fails to properly manage memory allocation and deallocation sequences, leading to use-after-free conditions. The attack vector leverages the font rendering pipeline where browsers automatically process font files from web content, making this a remote code execution risk. The vulnerability's impact extends beyond simple memory corruption as it can potentially provide attackers with information disclosure through Developer Console access or enable more sophisticated attacks through unspecified additional impacts.
From an operational perspective, this vulnerability poses significant risks to web browsing security as it allows remote attackers to exploit the font processing subsystem without user interaction. The attack requires only that a victim visits a malicious website containing crafted font content, making it particularly dangerous for web-based attacks. The OpenType Sanitiser's role in processing font data means that this vulnerability affects a core browser functionality that is widely used across the internet. Security researchers have classified this as a high-severity issue due to its potential for remote code execution and information disclosure, with the use-after-free pattern being particularly concerning as it can lead to arbitrary code execution in memory contexts.
Organizations and users should immediately update to Firefox version 36.0 or later to address this vulnerability, as the fix involves proper memory management within the font parsing code. The remediation addresses the root cause by implementing correct memory allocation and deallocation practices in the ots_gasp_parse function, preventing the access of freed memory locations. This vulnerability aligns with CWE-416 which defines use-after-free conditions as a common memory safety issue, and could potentially map to ATT&CK technique T1059.007 for exploitation through application-specific vulnerabilities. The fix demonstrates the importance of proper input validation and memory management in font processing libraries, as similar issues in font handling have been observed in other browser implementations and operating systems. Security teams should monitor for indicators of compromise related to malicious font content and ensure comprehensive patch management across all browser installations to prevent exploitation of this memory safety vulnerability.