CVE-2016-4320 in Bitbucket Server
Summary
by MITRE
Atlassian Bitbucket Server before 4.7.1 allows remote attackers to read the first line of an arbitrary file via a directory traversal attack on the pull requests resource.
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Analysis
by VulDB Data Team • 08/28/2020
Atlassian Bitbucket Server version 4.7.1 and earlier contains a critical directory traversal vulnerability that enables remote attackers to access arbitrary files on the underlying filesystem through the pull requests resource. This vulnerability falls under the CWE-22 category, which specifically addresses directory traversal attacks where attackers can manipulate file paths to access files outside of intended directories. The flaw exists in the way the application handles file path resolution when processing pull request requests, allowing malicious users to craft requests that traverse the filesystem hierarchy and retrieve sensitive information from the server.
The technical implementation of this vulnerability exploits the lack of proper input validation and path sanitization in the pull request handling component of Bitbucket Server. Attackers can construct malicious URLs that include directory traversal sequences such as ../ or ..\ to navigate to parent directories and access files that should remain protected. When a user submits a pull request request with manipulated file paths, the server fails to properly validate these inputs, allowing the traversal to occur and returning the contents of the requested files to the attacker. This particularly affects configuration files, log files, and potentially credential files that might be stored on the server filesystem.
The operational impact of this vulnerability is significant as it provides attackers with unauthorized access to sensitive data that could include system configurations, user credentials, application settings, and potentially source code repositories. The vulnerability affects organizations using Bitbucket Server in their development workflows, potentially exposing intellectual property and compromising the integrity of their software development processes. Remote exploitation means that attackers do not require physical access or network credentials to exploit this vulnerability, making it particularly dangerous for organizations that do not properly isolate their Bitbucket Server instances. The attack can be executed from any location with network access to the Bitbucket Server instance, making it a persistent threat that can be exploited repeatedly.
Organizations should immediately apply the patch released in Bitbucket Server version 4.7.1 to address this vulnerability. The mitigation strategy should include implementing proper input validation and path sanitization controls, restricting network access to Bitbucket Server instances through firewalls, and monitoring for suspicious access patterns in server logs. Security teams should also consider implementing web application firewalls to detect and block directory traversal attempts, while conducting regular security assessments of their Bitbucket Server deployments. This vulnerability aligns with the ATT&CK technique T1083 for discovering file and directory permissions, and T1566 for credential access through exploitation of web applications. Organizations should also review their access controls and implement principle of least privilege to minimize the impact of potential exploitation. The vulnerability demonstrates the importance of input validation in web applications and highlights the need for comprehensive security testing of all file access mechanisms within enterprise software platforms.