CVE-2017-7475 in Cairo
Summary
by MITRE
Cairo version 1.15.4 is vulnerable to a NULL pointer dereference related to the FT_Load_Glyph and FT_Render_Glyph resulting in an application crash.
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Analysis
by VulDB Data Team • 09/30/2020
The vulnerability identified as CVE-2017-7475 affects the Cairo graphics library version 1.15.4 and represents a critical NULL pointer dereference condition that can lead to application crashes. This issue manifests within the font rendering subsystem where the FT_Load_Glyph and FT_Render_Glyph functions fail to properly validate pointer references before attempting to access memory locations. The flaw occurs when the library processes certain malformed or specially crafted font files that cause the FreeType library components to return NULL pointers, which are subsequently dereferenced without proper null checks. This vulnerability falls under the category of improper error handling and memory management issues that are commonly classified as CWE-476, which specifically addresses NULL pointer dereference conditions.
The technical execution of this vulnerability involves the Cairo library's interaction with the FreeType font rendering engine where font glyphs are loaded and rendered. When the FT_Load_Glyph function encounters certain font data structures that result in a NULL return value, the subsequent FT_Render_Glyph call attempts to operate on this invalid pointer, causing the application to crash with a segmentation fault or access violation. This behavior can be exploited by attackers who craft malicious font files or manipulate font data in ways that trigger the specific code path leading to the NULL pointer dereference. The vulnerability demonstrates a classic weakness in defensive programming practices where error conditions are not properly handled before memory access operations occur.
From an operational perspective, this vulnerability presents significant risks to applications that rely on Cairo for graphics rendering, particularly those that process untrusted font data from external sources. Web browsers, office suites, graphic design applications, and any software that renders text using the Cairo library are potentially vulnerable to denial of service attacks. The crash behavior can be leveraged to cause application instability, leading to service disruption and potential exploitation for more severe attacks. The vulnerability's impact extends beyond simple application crashes as it can be used to disrupt legitimate user workflows and potentially provide a foothold for further exploitation attempts. Attackers could craft font files designed to trigger this specific crash condition, making it a valuable vector for remote code execution or privilege escalation scenarios.
Mitigation strategies for CVE-2017-7475 should focus on immediate patching of the Cairo library to version 1.15.10 or later, which contains the necessary fixes for the NULL pointer dereference issue. Organizations should also implement input validation measures that filter or sanitize font data before processing, particularly when handling external or untrusted sources. The implementation of proper error handling routines that check for NULL return values from FreeType functions before attempting to use the returned pointers provides an additional layer of defense. Security teams should monitor for applications that utilize Cairo and ensure they are updated to versions that address this vulnerability, while also considering the deployment of intrusion detection systems that can identify attempts to exploit this specific crash condition. This vulnerability aligns with ATT&CK technique T1203, which covers legitimate programs that can be used to execute malicious code, and demonstrates how graphics libraries can serve as attack vectors when proper input validation and error handling are not implemented.