CVE-2021-32557 in Apport
Summary
by MITRE • 06/12/2021
It was discovered that the process_report() function in data/whoopsie-upload-all allowed arbitrary file writes via symlinks.
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Analysis
by VulDB Data Team • 06/14/2021
The vulnerability identified as CVE-2021-32557 resides within the process_report() function in the data/whoopsie-upload-all component of a software system, representing a critical security flaw that enables unauthorized file modification through symbolic link manipulation. This issue specifically affects systems that utilize whoopsie for crash reporting and error handling, where the software processes uploaded crash reports and system logs. The vulnerability stems from insufficient validation of file paths and symbolic link handling within the upload processing pipeline, creating a path traversal condition that allows attackers to manipulate the file system beyond intended boundaries.
The technical implementation of this vulnerability involves the improper handling of symbolic links during the file processing workflow. When the process_report() function encounters a file path that contains symbolic links, it fails to properly resolve or validate these links before performing write operations. This allows an attacker to create malicious symbolic links that point to sensitive system files or directories outside the intended processing scope. The flaw essentially permits arbitrary file write operations by exploiting the trust placed in the file path resolution mechanism, enabling attackers to overwrite critical system files or inject malicious content into otherwise protected locations. This type of vulnerability aligns with CWE-22 Path Traversal and CWE-73 Path Traversal via Symlink, demonstrating how symbolic link manipulation can bypass traditional file access controls.
The operational impact of CVE-2021-32557 extends beyond simple file corruption, as it provides attackers with potential persistence mechanisms and privilege escalation opportunities within affected systems. An attacker who successfully exploits this vulnerability could overwrite system binaries, configuration files, or log files, potentially leading to system compromise, data exfiltration, or service disruption. The vulnerability is particularly concerning in environments where whoopsie is used for automated crash reporting, as it could be exploited during routine system operations without requiring explicit user interaction. This makes the attack surface broader and more difficult to detect, as the malicious file operations would appear to be legitimate system processes. The vulnerability also aligns with ATT&CK technique T1059 Command and Scripting Interpreter, where attackers might leverage the compromised system to execute malicious code through manipulated file writes, and T1566 Phishing, as attackers could use this vulnerability to establish persistence through modified system files.
Mitigation strategies for CVE-2021-32557 should focus on implementing robust input validation and path resolution mechanisms that properly handle symbolic links. System administrators should ensure that the whoopsie-upload-all component validates all file paths before processing and avoids following symbolic links during file operations. The recommended approach includes implementing strict path validation that rejects any input containing symbolic links or relative path components, and using absolute paths with proper access control checks. Additionally, privilege separation should be enforced so that the file processing component runs with minimal required permissions, reducing the potential impact of successful exploitation. Organizations should also implement monitoring and alerting for unusual file modification patterns and ensure that all systems running whoopsie are kept up to date with security patches. The vulnerability demonstrates the importance of proper sandboxing and access control in system components that handle user-supplied data, as highlighted in security frameworks such as the NIST Cybersecurity Framework and ISO 27001 standards for information security management.