CVE-2021-39596 in swftools
Summary
by MITRE • 09/20/2021
An issue was discovered in swftools through 20200710. A NULL pointer dereference exists in the function code_parse() located in code.c. It allows an attacker to cause Denial of Service.
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Analysis
by VulDB Data Team • 09/30/2021
The vulnerability identified as CVE-2021-39596 represents a critical NULL pointer dereference flaw within the swftools software suite, specifically affecting versions through 20200710. This issue manifests within the code_parse() function situated in the code.c source file, creating a scenario where maliciously crafted input can trigger unexpected program termination. The swftools package serves as a comprehensive collection of utilities for working with flash files and multimedia content, making it a widely used tool in various environments including web development, multimedia production, and content analysis systems. The NULL pointer dereference vulnerability occurs when the function attempts to access memory through a pointer that has not been properly initialized or has been set to NULL, leading to immediate program crash and system instability.
From a technical perspective, the flaw in code_parse() function demonstrates a classic programming error pattern that falls under CWE-476, which specifically addresses NULL pointer dereference conditions. This vulnerability type represents one of the most common and dangerous classes of software defects, as it can be exploited to cause system instability and denial of service conditions without requiring elevated privileges. The function's failure to properly validate pointer states before dereferencing creates an exploitable condition where an attacker can craft input data that will cause the program to attempt accessing memory at address zero, resulting in immediate segmentation fault or access violation. The vulnerability is particularly concerning because it operates at the core parsing functionality level, meaning that any attempt to process SWF files through this tool could trigger the malicious behavior.
The operational impact of CVE-2021-39596 extends beyond simple denial of service, as it can severely disrupt workflows in environments where swftools is utilized for automated processing or content analysis. Organizations that rely on this tool for SWF file manipulation, conversion, or inspection may experience complete service outages when malicious input is processed, potentially affecting web applications, multimedia content management systems, or automated testing frameworks. The vulnerability can be exploited through various attack vectors including malicious SWF files uploaded to web applications, automated file processing pipelines, or even through command line interfaces where users might inadvertently process compromised content. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion or application crashes, making it particularly dangerous in environments where automated processing occurs without proper input validation.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected swftools versions to the latest releases where the NULL pointer dereference has been corrected. System administrators should implement input validation measures to prevent untrusted SWF content from being processed through the affected tool, including the deployment of sandboxed environments or content filtering mechanisms. Additionally, monitoring systems should be configured to detect unusual process termination patterns that might indicate exploitation attempts. The remediation process should also include comprehensive testing of all SWF processing workflows to ensure that the vulnerability has been fully addressed and that no other similar flaws exist within the codebase. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to reduce the effectiveness of potential exploitation attempts, while maintaining regular vulnerability assessments to identify similar issues in other software components.