CVE-2019-9686 in Pacman
Summary
by MITRE
pacman before 5.1.3 allows directory traversal when installing a remote package via a specified URL "pacman -U <url>" due to an unsanitized file name received from a Content-Disposition header. pacman renames the downloaded package file to match the name given in this header. However, pacman did not sanitize this name, which may contain slashes, before calling rename(). A malicious server (or a network MitM if downloading over HTTP) can send a Content-Disposition header to make pacman place the file anywhere in the filesystem, potentially leading to arbitrary root code execution. Notably, this bypasses pacman's package signature checking. This occurs in curl_download_internal in lib/libalpm/dload.c.
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Analysis
by VulDB Data Team • 07/31/2023
The vulnerability identified as CVE-2019-9686 represents a critical directory traversal flaw in the pacman package manager version 5.1.2 and earlier. This security issue arises from improper handling of file names received from HTTP Content-Disposition headers during remote package installation processes. The flaw specifically manifests when users execute pacman commands with remote package URLs using the -U flag, creating a dangerous attack vector that can be exploited by malicious actors controlling remote servers or network intermediaries.
The technical implementation of this vulnerability stems from the download function within pacman's libalpm/dload.c library where curl_download_internal processes package downloads. When a remote server responds with a Content-Disposition header containing a filename, pacman directly uses this value without sanitizing it to remove potentially dangerous characters such as forward slashes. This unsanitized filename is then passed to the rename() system call, allowing attackers to specify arbitrary filesystem paths. The vulnerability is particularly dangerous because it bypasses pacman's built-in package signature verification mechanisms, meaning that even if a package is signed, the malicious file placement can still occur.
The operational impact of this vulnerability extends beyond simple file placement issues and can lead to arbitrary code execution with root privileges. Attackers can craft Content-Disposition headers that place malicious files in critical system locations such as /usr/bin or other execution paths, effectively enabling privilege escalation attacks. The vulnerability is especially severe when network traffic is not properly secured, as man-in-the-middle attackers can intercept HTTP connections and modify the Content-Disposition headers without requiring any authentication or authorization. This makes the attack surface particularly broad in environments where HTTP is used for package management without proper TLS enforcement.
This vulnerability maps directly to CWE-22 - Improper Limitation of a Pathname to a Restricted Directory, which classifies path traversal issues that allow attackers to access files or directories outside of intended boundaries. The attack pattern aligns with ATT&CK technique T1059.007 - Command and Scripting Interpreter: Python, where adversaries can leverage directory traversal to execute malicious code through package installation processes. The security implications are further compounded by the fact that this flaw affects the core package management functionality that is fundamental to system security, making it a critical target for exploitation in compromise scenarios. Organizations using vulnerable versions of pacman should immediately implement mitigations including upgrading to version 5.1.3 or later, enforcing HTTPS for all package downloads, and implementing network-level protections against malicious Content-Disposition headers to prevent exploitation of this vulnerability.