CVE-2020-36123 in libsixel
Summary
by MITRE • 03/10/2022
saitoha libsixel v1.8.6 was discovered to contain a double free via the component sixel_chunk_destroy at /root/libsixel/src/chunk.c.
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Analysis
by VulDB Data Team • 03/12/2022
The vulnerability identified as CVE-2020-36123 affects saitoha libsixel version 1.8.6 and represents a critical double free error within the sixel_chunk_destroy function located in the chunk.c source file. This memory corruption issue arises when the library processes certain input data through the sixel format handling mechanisms, creating conditions where the same memory block gets freed twice during the cleanup process. The flaw occurs in the chunk management subsystem that handles the decompression and rendering of sixel graphics data, which are commonly used for terminal-based image display in legacy systems and certain specialized applications.
The technical implementation of this vulnerability stems from improper memory management within the sixel_chunk_destroy function where the library fails to properly track memory allocation states during the destruction of chunk objects. When processing malformed or specially crafted sixel data streams, the function executes multiple free operations on the same memory address, leading to a double free condition that can result in heap corruption. This type of vulnerability falls under CWE-415, which specifically addresses double free conditions in memory management, and can be classified as a heap-based memory corruption issue. The vulnerability is particularly concerning because it can be triggered through user-supplied input data that gets parsed and processed by the library, making it exploitable in scenarios where the library handles untrusted sixel formatted content.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can potentially enable remote code execution or denial of service conditions depending on the environment where the affected library is deployed. Applications that utilize libsixel for image rendering in terminal environments, such as certain terminal emulators, text-based image viewers, or legacy system interfaces, become vulnerable to exploitation. The vulnerability can be leveraged by attackers who can craft malicious sixel data streams that trigger the double free condition during processing, potentially leading to arbitrary code execution or system instability. This is particularly relevant in environments where the library processes content from untrusted sources, such as web applications, email clients, or file processing systems that handle various graphic formats.
Mitigation strategies for CVE-2020-36123 should prioritize immediate patching of the affected libsixel library to version 1.8.7 or later, which contains the necessary memory management fixes. System administrators should also implement input validation and sanitization measures when processing sixel formatted content, particularly in applications that accept user uploads or external data streams. The implementation of address sanitization tools and memory debugging utilities can help detect similar issues in other library components. From an operational security perspective, network segmentation and privilege separation should be maintained to limit potential exploitation impact. Additionally, monitoring systems should be configured to detect unusual memory allocation patterns or application crashes that may indicate exploitation attempts. Organizations using this library should also consider implementing runtime protections such as stack canaries, address space layout randomization, and control flow integrity mechanisms to further reduce the exploitability of such memory corruption vulnerabilities. The ATT&CK framework categorizes this vulnerability under T1059.007 for command and scripting interpreter, as exploitation may involve crafting specific input to trigger the memory corruption, and potentially T1499.004 for network denial of service if the vulnerability is used to crash services.