CVE-2012-5670 in FreeType
Summary
by MITRE
The _bdf_parse_glyphs function in FreeType before 2.4.11 allows context-dependent attackers to cause a denial of service (out-of-bounds write and crash) via vectors related to BDF fonts and an ENCODING field with a negative value.
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Analysis
by VulDB Data Team • 12/21/2021
The vulnerability identified as CVE-2012-5670 resides within the FreeType font rendering library, specifically in the _bdf_parse_glyphs function that handles Bitmapped Font (BDF) format parsing. This critical flaw affects FreeType versions prior to 2.4.11 and represents a classic buffer overflow condition that can be exploited through malformed BDF font files. The vulnerability manifests when the ENCODING field within BDF fonts contains a negative value, creating a context-dependent attack vector that allows remote adversaries to manipulate the font parsing process. The issue stems from insufficient input validation and boundary checking within the glyph parsing routine, where the software fails to properly validate the encoding values before using them to calculate memory offsets. This vulnerability falls under CWE-129, which specifically addresses insufficient validation of length fields, and represents a subtype of out-of-bounds write conditions that can lead to arbitrary code execution or system instability. The attack requires an adversary to craft a malicious BDF font file with a negative ENCODING value, which when processed by the vulnerable FreeType library causes the application to write data beyond the allocated memory boundaries, ultimately resulting in application crashes or potential system compromise.
The operational impact of CVE-2012-5670 extends across numerous applications and systems that rely on FreeType for font rendering, including web browsers, desktop applications, graphic design software, and server applications that process user-uploaded font files. When exploited, this vulnerability can cause denial of service conditions that render applications unusable, potentially leading to complete system crashes in scenarios where the vulnerable applications are running with elevated privileges. The context-dependent nature of the attack means that exploitation is possible in environments where users can upload or access BDF font files, making it particularly dangerous in web applications, email clients, and content management systems. The vulnerability aligns with ATT&CK technique T1203, which describes exploitation of software vulnerabilities for denial of service, and can be leveraged as part of broader attack chains where initial access is achieved through other means but the vulnerability serves to maintain persistence or escalate privileges. The out-of-bounds write condition creates a predictable crash pattern that can be used for both service disruption and potentially more advanced exploitation techniques, depending on the target system's memory layout and protection mechanisms.
Mitigation strategies for CVE-2012-5670 primarily focus on immediate remediation through software updates and patches, with the most effective solution being the upgrade to FreeType version 2.4.11 or later, which contains the necessary fixes for the BDF parsing logic. System administrators should prioritize patching all affected applications that utilize FreeType, particularly those handling user-provided content or external font files. Additional protective measures include implementing strict input validation for font files, deploying application whitelisting policies, and configuring sandboxing mechanisms around font processing components. Network-level defenses such as web application firewalls can be configured to block or scan for suspicious font file content, while monitoring systems should be implemented to detect unusual application crash patterns or memory access violations. Organizations should also conduct comprehensive vulnerability assessments to identify all systems and applications that may be affected by this vulnerability, particularly those that process untrusted font data. The fix implemented in FreeType 2.4.11 involves proper validation of the ENCODING field values and implementation of robust boundary checks before any memory operations are performed, preventing the out-of-bounds write conditions that previously enabled exploitation. Regular security audits and vulnerability management processes should include verification of FreeType library versions across all systems to prevent recurrence of similar issues in the future.