CVE-2012-2840 in libexif
Summary
by MITRE
Off-by-one error in the exif_convert_utf16_to_utf8 function in exif-entry.c in the EXIF Tag Parsing Library (aka libexif) before 0.6.21 allows remote attackers to cause a denial of service or possibly execute arbitrary code via crafted EXIF tags in an image.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 12/06/2021
The vulnerability CVE-2012-2840 represents a critical off-by-one error within the exif_convert_utf16_to_utf8 function in libexif's exif-entry.c module. This flaw exists in versions prior to 0.6.21 of the EXIF Tag Parsing Library, which is widely used for parsing and processing EXIF metadata in digital images. The vulnerability stems from improper boundary checking during the conversion process between UTF-16 and UTF-8 character encodings, creating a potential buffer overflow condition that can be exploited through maliciously crafted EXIF metadata.
The technical implementation of this vulnerability occurs when the exif_convert_utf16_to_utf8 function processes UTF-16 encoded strings within EXIF tags without adequate validation of string boundaries. An attacker can construct specially formatted EXIF data containing malformed UTF-16 sequences that cause the function to read or write beyond allocated memory boundaries. This off-by-one error specifically affects the memory management during character encoding conversion, where the function fails to properly account for the exact byte boundaries when processing Unicode characters. The flaw is categorized under CWE-129 as an improper validation of array indices, and more specifically as CWE-125 when considering the potential for out-of-bounds memory access.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable remote code execution in vulnerable applications. When exploited, the off-by-one error can cause application crashes through heap corruption, leading to denial of service conditions that affect image processing applications, web servers handling image uploads, or any system that relies on libexif for metadata parsing. However, the more serious implications arise when the vulnerability is leveraged in conjunction with other exploit techniques, potentially allowing attackers to execute arbitrary code on affected systems. The ATT&CK framework would classify this as a code injection technique under T1059, specifically targeting the application layer through malformed input processing.
Systems most at risk include web applications that accept user-uploaded images without proper validation, content management systems processing EXIF data, digital asset management platforms, and image processing libraries that depend on libexif. The vulnerability affects any software that parses EXIF metadata from image files, including but not limited to web servers, image viewers, social media platforms, and mobile applications that handle photo uploads. Security researchers have noted that the exploitability of this vulnerability is heightened in environments where applications do not implement proper input sanitization or where the affected libraries are used in unpatched applications.
Mitigation strategies should focus on immediate patching of libexif to version 0.6.21 or later, which contains the necessary boundary checks to prevent the off-by-one error. Organizations should implement comprehensive input validation for all image metadata processing, particularly when handling user-uploaded content, and consider deploying sandboxing techniques for image processing operations. Network security controls should include monitoring for unusual image processing patterns that might indicate exploitation attempts, while application-level defenses should incorporate proper error handling and memory management practices. The vulnerability also underscores the importance of regular security updates and dependency management, as this flaw existed for several years before being properly addressed in the patched version. Additionally, implementing automated scanning tools that can detect malformed EXIF data in image files provides an additional layer of protection against exploitation attempts.