CVE-2021-42201 in swftools
Summary
by MITRE • 06/02/2022
An issue was discovered in swftools through 20201222. A heap-buffer-overflow exists in the function swf_GetD64() located in rfxswf.c. It allows an attacker to cause code execution.
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Analysis
by VulDB Data Team • 06/05/2022
The vulnerability identified as CVE-2021-42201 represents a critical heap buffer overflow flaw within the swftools software suite, specifically affecting versions through 20201222. This issue resides within the swf_GetD64() function located in the rfxswf.c source file, making it a significant concern for systems that process or handle swf file formats. The heap buffer overflow occurs when the application processes malformed or specially crafted input data, creating conditions where memory corruption can occur beyond the bounds of allocated heap memory regions. Such vulnerabilities are particularly dangerous because they can be exploited to execute arbitrary code, potentially leading to complete system compromise.
The technical nature of this vulnerability places it squarely within CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. This type of vulnerability typically arises from inadequate input validation and memory management practices during the parsing of binary file formats. The swftools package, designed for processing flash movie files, processes various data structures that may not properly validate the size or format of incoming data before attempting to read or manipulate it. When the swf_GetD64() function encounters malformed data, it fails to properly bounds-check memory access, allowing attackers to craft specific swf files that trigger the overflow condition.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it enables remote code execution capabilities that can be leveraged by malicious actors. Attackers can exploit this flaw by preparing specially crafted swf files that, when processed by vulnerable software, will trigger the heap overflow and potentially allow for arbitrary code execution on the target system. This makes the vulnerability particularly dangerous in environments where swf files are processed automatically or where users can upload or download swf content. The exploitability of this vulnerability is enhanced by the fact that it can be triggered through normal file processing operations without requiring special privileges or complex attack vectors.
Mitigation strategies for CVE-2021-42201 should prioritize immediate software updates to versions that have addressed the heap buffer overflow issue. Organizations should implement comprehensive input validation and sanitization measures for any swf file processing systems, including the use of memory-safe programming practices and runtime protections such as address space layout randomization. The vulnerability also highlights the importance of regular security assessments and vulnerability management processes, particularly for software packages that handle binary file formats. Additionally, implementing network segmentation and access controls can limit the potential impact of successful exploitation attempts, while monitoring systems should be deployed to detect unusual file processing activities that might indicate exploitation attempts. The ATT&CK framework categorizes this type of vulnerability under T1059 for execution through command and script interpreters, and T1203 for exploitation of software vulnerabilities, emphasizing the need for layered defensive strategies.