CVE-2026-55798 in Pillow
Summary
by MITRE • 07/06/2026
Pillow is a Python imaging library. Prior to 12.3.0, WindowsViewer.get_command() constructed a cmd.exe shell command by directly embedding a file path into an f-string without escaping and passed the result to subprocess.Popen(..., shell=True), allowing shell metacharacters in the file path to inject arbitrary cmd.exe commands. This issue is fixed in version 12.3.0.
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Analysis
by VulDB Data Team • 07/06/2026
The Pillow library presents a critical command injection vulnerability through its WindowsViewer.get_command() method that affects versions prior to 12.3.0. This flaw stems from improper input validation and sanitization when constructing shell commands on Windows systems, creating an avenue for malicious code execution through carefully crafted file paths. The vulnerability manifests when the library processes image files through the Windows viewer functionality, which relies on executing system commands via subprocess.Popen with shell=True parameter.
The technical implementation of this vulnerability involves direct string interpolation using f-strings without proper escaping or sanitization of user-supplied file paths. When a malicious actor provides a file path containing shell metacharacters such as ampersands, semicolons, or other command separators, these characters are interpreted by the cmd.exe shell rather than treated as literal filename characters. This creates a classic command injection scenario where arbitrary system commands can be executed with the privileges of the process running the Pillow library.
This vulnerability aligns with CWE-78, which specifically addresses improper neutralization of special elements used in OS commands, and represents a variant of the broader category of shell injection flaws. The operational impact extends beyond simple privilege escalation as it allows attackers to execute arbitrary code on affected systems, potentially leading to complete system compromise. The vulnerability is particularly dangerous in environments where Pillow processes untrusted image files from web applications, file uploads, or other user-provided content sources.
The attack surface expands significantly when considering that many applications use Pillow for image processing tasks including web applications, automated image analysis tools, and document management systems. An attacker could exploit this by uploading a specially crafted image file with a malicious path containing shell injection sequences. The vulnerability is classified under ATT&CK technique T1059.003 for command and scripting interpreter and T1203 for Exploitation for Client Execution, making it particularly relevant in modern threat landscape analysis.
Mitigation strategies require immediate upgrading to Pillow version 12.3.0 or later where the vulnerability has been patched through proper input sanitization and command construction methods. Organizations should also implement additional defensive measures including restricting file upload capabilities, validating image file formats, and employing sandboxing techniques for image processing operations. Network segmentation and privilege separation can help limit the potential damage from successful exploitation attempts, while monitoring for unusual system command execution patterns can aid in early detection of exploitation attempts.