CVE-2026-110650 in Thumbnail
Summary
by MITRE • 10/15/2026
The thumbnail Python package through 1.5 contains an OS command injection vulnerability in generate_thumbnail() that allows attackers to execute commands by supplying shell metacharacters in file paths. Attackers who control a file name passed to generate_thumbnail, such as an uploaded file, can inject commands into os.system() calls running ffmpeg, convert or unoconv with the Python process privileges.
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Analysis
by VulDB Data Team • 10/15/2026
The thumbnail library for Python versions up through 1.5 contains a critical operating system command injection vulnerability within its core image processing functionality. This flaw specifically resides in the generate_thumbnail function, which is designed to create scaled-down representations of images and documents. The root cause of this security issue lies in how the application constructs shell commands when invoking external multimedia conversion tools such as ffmpeg, ImageMagick convert, or LibreOffice unoconv. Instead of using safe programmatic interfaces that pass arguments directly to these executables without involving a command interpreter, the library relies on os.system calls with string formatting that includes user-supplied file paths. This architectural decision creates a direct pathway for attackers to inject arbitrary operating system commands if they can control any part of the filename or path provided as input to the function.
The technical mechanism behind this vulnerability exploits the shell metacharacters interpreted by the underlying command line environment, typically bash on Linux systems or cmd.exe on Windows. When an attacker supplies a file name containing characters such as semicolons, pipes, ampersands, or backticks, these symbols are passed directly into the os.system string without proper sanitization or escaping. For instance, if a user uploads a file named report.pdf; rm -rf /, and this filename is processed by generate_thumbnail, the resulting command executed might look like ffmpeg -i "report.pdf; rm -rf /" ... The shell interprets the semicolon as a command separator, causing it to execute the malicious payload immediately after attempting to process the intended file. This behavior allows for remote code execution with the same privileges as the Python process running the thumbnail generation service.
The operational impact of this vulnerability is severe, particularly in web applications or services that accept user-uploaded files and automatically generate thumbnails for display purposes. An attacker who can upload a maliciously named file can achieve arbitrary command execution on the host system. This could lead to complete compromise of the server, including data exfiltration, installation of backdoors, pivoting to other internal systems, or denial of service through resource exhaustion. Since many web applications run with elevated privileges to access files and databases, successful exploitation often results in full control over the underlying operating environment. The risk is amplified because thumbnail generation is a common feature in content management systems, social media platforms, and document sharing services, making it a frequent target for automated scanning tools seeking easy entry points into application infrastructure.
This vulnerability aligns with CWE-78 Improper Neutralization of Special Elements used in an OS Command commonly known as OS Command Injection. It also maps to MITRE ATT&CK technique T1059 Command and Scripting Interpreter, specifically subtechniques involving shell commands for lateral movement or persistence depending on the payload delivered. To mitigate this risk, developers should immediately upgrade to a patched version of the thumbnail package where available. If upgrading is not feasible, immediate remediation requires replacing os.system calls with subprocess.run using list arguments rather than string shells, which prevents the shell from interpreting metacharacters as command delimiters. Additionally implementing strict input validation that rejects filenames containing special characters or restricting allowed file extensions can provide defense in depth. Security teams should also audit existing codebases for similar patterns where external commands are constructed via string concatenation involving user-controlled data and apply parameterized execution methods consistently across all image processing modules.