CVE-2017-7777 in Firefox
Summary
by MITRE
Use of uninitialized memory in Graphite2 library in Firefox before 54 in graphite2::GlyphCache::Loader::read_glyph function.
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Analysis
by VulDB Data Team • 05/29/2020
The vulnerability identified as CVE-2017-7777 represents a critical memory safety issue within the Graphite2 library implementation in Mozilla Firefox browsers prior to version 54. This flaw exists specifically within the graphite2::GlyphCache::Loader::read_glyph function where uninitialized memory is being accessed during font rendering operations. The Graphite2 library serves as a sophisticated text shaping engine that handles complex typography and font rendering for various writing systems, particularly those requiring sophisticated glyph positioning and substitution algorithms. When Firefox processes web content containing specially crafted fonts or text elements, the uninitialized memory access can lead to unpredictable behavior and potential exploitation.
The technical nature of this vulnerability stems from improper initialization of memory variables within the glyph caching mechanism that Firefox employs when processing complex text layouts. During normal operation, the Graphite2 library maintains a cache of pre-computed glyph information to optimize rendering performance. However, in the affected Firefox versions, the read_glyph function fails to properly initialize certain memory regions before accessing them, creating a scenario where sensitive data from previous operations or memory garbage could be inadvertently read and processed. This uninitialized memory access creates a potential pathway for information disclosure and could be leveraged to execute arbitrary code within the browser context.
The operational impact of CVE-2017-7777 extends beyond simple memory corruption, as it represents a fundamental flaw in how Firefox handles complex typography rendering. Attackers could potentially craft malicious web pages containing specially formatted fonts or text elements that trigger the uninitialized memory access when the browser attempts to render the content. This vulnerability aligns with CWE-457, which specifically addresses the use of uninitialized variables, and demonstrates how such issues can escalate into more serious security concerns when they occur in critical rendering components. The attack surface is particularly concerning given that font rendering is a common operation in web browsing, making exploitation relatively straightforward through standard web page delivery mechanisms.
The exploitation of this vulnerability could potentially allow attackers to extract sensitive information from memory, manipulate the browser's rendering behavior, or in more sophisticated scenarios, achieve remote code execution. This aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as the vulnerability could be leveraged to execute arbitrary code in the browser process. Organizations and users operating Firefox versions prior to 54 should immediately implement mitigations including updating to the patched version, which properly initializes memory variables within the Graphite2 library. Additionally, browser hardening measures such as disabling complex font rendering features or implementing strict content security policies may provide additional defense in depth. The vulnerability serves as a reminder of the critical importance of memory safety in graphics and typography libraries, particularly those integrated into browser applications where they handle untrusted content from multiple sources.