CVE-2019-19635 in libsixel
Summary
by MITRE
An issue was discovered in libsixel 1.8.2. There is a heap-based buffer overflow in the function sixel_decode_raw_impl at fromsixel.c.
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Analysis
by VulDB Data Team • 03/09/2024
The vulnerability identified as CVE-2019-19635 represents a critical heap-based buffer overflow within the libsixel library version 1.8.2, specifically within the sixel_decode_raw_impl function located in the fromsixel.c source file. This flaw exists in the processing of SIXEL graphics format data, which is a graphics standard used primarily in terminal environments and legacy systems. The libsixel library serves as a decoder for SIXEL image format, commonly utilized in applications that need to display graphical content within terminal interfaces. The buffer overflow occurs during the decoding process when the library fails to properly validate input data length against allocated memory boundaries, creating a potential exploitation vector for malicious actors.
The technical nature of this vulnerability stems from inadequate bounds checking within the sixel_decode_raw_impl function, which processes raw SIXEL data streams. When malformed or oversized input data is provided to the library, the implementation attempts to write data beyond the allocated heap memory region, potentially overwriting adjacent memory blocks. This heap corruption can lead to arbitrary code execution, application crashes, or denial of service conditions. The vulnerability manifests when the library processes specially crafted SIXEL input that exceeds the expected buffer size, causing the memory allocator to overwrite adjacent heap chunks. The flaw is classified as a heap-based buffer overflow under CWE-121, which specifically addresses heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite heap memory.
From an operational perspective, this vulnerability poses significant risks to systems that utilize libsixel for image processing, particularly in terminal-based applications, remote access tools, or any software that accepts SIXEL formatted input from untrusted sources. Attackers could exploit this weakness by crafting malicious SIXEL data streams that trigger the buffer overflow during decoding operations. The impact extends beyond simple application crashes, as successful exploitation could enable privilege escalation or remote code execution depending on the target system's security context. The vulnerability affects any application using libsixel version 1.8.2 or earlier, including terminal emulators, file viewers, and legacy communication software that handle SIXEL graphics. This flaw aligns with ATT&CK technique T1203, which involves exploiting weaknesses in input validation and memory management to achieve code execution.
Mitigation strategies for CVE-2019-19635 primarily focus on immediate software updates to libsixel version 1.8.3 or later, which contains the necessary patches to address the heap overflow condition. Organizations should prioritize patching affected systems and applications that depend on the vulnerable library, particularly in environments where untrusted SIXEL data may be processed. Additional defensive measures include implementing input validation mechanisms, restricting SIXEL data sources to trusted origins, and deploying runtime protections such as address space layout randomization and stack canaries. System administrators should monitor for exploitation attempts through log analysis and implement network segmentation to limit the potential impact of successful attacks. The vulnerability demonstrates the importance of proper memory management practices and input validation in security-critical libraries, emphasizing that even seemingly benign graphics processing functions can present significant security risks when proper bounds checking is absent.