CVE-2018-5248 in ImageMagick
Summary
by MITRE
In ImageMagick 7.0.7-17 Q16, there is a heap-based buffer over-read in coders/sixel.c in the ReadSIXELImage function, related to the sixel_decode function.
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Analysis
by VulDB Data Team • 01/20/2023
The vulnerability identified as CVE-2018-5248 represents a critical heap-based buffer over-read flaw within ImageMagick's SIXEL image processing functionality. This issue specifically affects ImageMagick version 7.0.7-17 Q16 and stems from improper memory management in the coders/sixel.c file, where the ReadSIXELImage function fails to adequately validate input data before processing. The vulnerability manifests through the sixel_decode function which handles SIXEL format image decoding, creating a scenario where maliciously crafted SIXEL files can trigger unauthorized memory access patterns that extend beyond allocated buffer boundaries.
The technical implementation of this vulnerability involves the manipulation of SIXEL image data structures during the decoding process, where insufficient bounds checking allows attackers to read memory locations that should remain protected. This over-read condition occurs when the sixel_decode function processes malformed SIXEL data without proper validation of buffer limits, potentially exposing sensitive information stored in adjacent memory regions. The heap-based nature of the vulnerability indicates that the affected memory locations are dynamically allocated and managed by the application's memory heap, making the attack surface particularly dangerous as it can potentially reveal cryptographic keys, passwords, or other confidential data stored in nearby memory segments.
From an operational perspective, this vulnerability presents significant risk to systems processing untrusted image content, particularly in web applications, email servers, and document processing systems that utilize ImageMagick for image handling. Attackers can exploit this weakness by crafting malicious SIXEL files that, when processed by vulnerable ImageMagick installations, cause the application to read beyond intended memory boundaries. The impact extends beyond simple information disclosure, as this type of memory corruption can potentially lead to arbitrary code execution, especially when combined with other vulnerabilities or when the application runs with elevated privileges. The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and represents a clear example of how insufficient input validation in multimedia processing libraries can create dangerous attack vectors.
The mitigation strategy for CVE-2018-5248 requires immediate patching of ImageMagick installations to versions that address the buffer over-read issue in the sixel_decode function. Organizations should implement comprehensive input validation for all SIXEL image processing operations and consider disabling SIXEL format support entirely if it is not essential for business operations. Network segmentation and application whitelisting can provide additional protection layers, while monitoring for unusual memory access patterns and buffer over-read attempts should be enabled. Security teams should also consider implementing sandboxing mechanisms for image processing operations and ensure that ImageMagick runs with minimal required privileges to limit potential damage from successful exploitation attempts. This vulnerability demonstrates the critical importance of input validation in multimedia libraries and aligns with ATT&CK technique T1203, which covers exploitation for privilege escalation through memory corruption vulnerabilities.