CVE-2020-10177 in Pillow
Summary
by MITRE
Pillow before 6.2.3 and 7.x before 7.0.1 has multiple out-of-bounds reads in libImaging/FliDecode.c.
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Analysis
by VulDB Data Team • 05/05/2025
The vulnerability identified as CVE-2020-10177 affects the Pillow library, a popular Python imaging library used for processing various image formats. This issue manifests as multiple out-of-bounds read conditions within the libImaging/FliDecode.c component, which is responsible for decoding FLI (Flexible Image Layout Interface) format files. The affected versions include all releases prior to Pillow 6.2.3 and 7.0.1, representing a significant portion of the library's user base that could potentially be impacted by this memory safety issue.
The technical flaw stems from insufficient bounds checking during the parsing of FLI format files, specifically within the decoding routines that handle frame data and metadata structures. When processing malformed or maliciously crafted FLI files, the library fails to properly validate array indices and buffer boundaries before accessing memory locations. This vulnerability falls under CWE-129, which specifically addresses insufficient validation of length of inputs, and more broadly relates to CWE-125, which covers out-of-bounds read conditions. The root cause lies in the absence of proper input sanitization and boundary validation mechanisms within the FLI decoding logic, allowing attackers to manipulate memory access patterns through carefully constructed input data.
The operational impact of this vulnerability extends beyond simple memory corruption scenarios, as it can potentially enable remote code execution or denial of service conditions depending on the execution environment and how the library is utilized. When exploited, these out-of-bounds reads could allow attackers to access sensitive memory regions, potentially leading to information disclosure or system compromise. The vulnerability is particularly concerning in web applications and server environments where image processing is common, as it could be leveraged through file upload functionality or image manipulation services. This aligns with ATT&CK technique T1203, which covers exploitation of vulnerabilities in software libraries and frameworks that are commonly used in application environments.
Organizations utilizing Pillow in their applications should immediately upgrade to version 6.2.3 or 7.0.1 to mitigate this vulnerability. The fix implemented in these versions includes enhanced input validation and proper bounds checking within the FLI decoding routines. Additional mitigations should include implementing strict file type validation, limiting file upload capabilities, and employing sandboxed execution environments for image processing operations. Security monitoring should also be enhanced to detect anomalous image processing patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date third-party libraries and implementing robust input validation practices across all software components that handle external data processing.