CVE-2011-4407 in Ubuntu Linux
Summary
by MITRE
ppa.py in Software Properties before 0.81.13.3 does not validate the server certificate when downloading PPA GPG key fingerprints, which allows man-in-the-middle (MITM) attackers to spoof GPG keys for a package repository.
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Analysis
by VulDB Data Team • 01/05/2025
The vulnerability described in CVE-2011-4407 resides within the software properties package manager component of Ubuntu and Debian systems, specifically in the ppa.py script that handles package repository management. This flaw represents a critical security weakness in the package management infrastructure that affects systems using the software-properties package version 0.81.13.2 and earlier. The vulnerability enables malicious actors to perform man-in-the-middle attacks against the package repository signing process, compromising the integrity of software distribution mechanisms that rely on GPG key verification.
The technical implementation of this vulnerability stems from insufficient certificate validation during the GPG key fingerprint download process from Launchpad PPAs. When users attempt to add new package repositories through the software-properties interface, the ppa.py script downloads GPG key fingerprints from remote servers without properly validating the server certificates. This absence of certificate validation creates an attack surface where adversaries can intercept network traffic between the client and the legitimate PPA server, presenting forged certificate information to the client. The flaw essentially allows attackers to substitute their own GPG keys for legitimate repository keys, enabling them to sign malicious packages that will be accepted as authentic by the system.
The operational impact of this vulnerability extends beyond simple package integrity concerns, as it fundamentally undermines the trust model that package managers rely upon for secure software distribution. When an attacker successfully spoofs a GPG key, they can inject malicious packages into the target system that will be accepted without warning, potentially leading to arbitrary code execution, privilege escalation, or complete system compromise. The vulnerability affects not only individual user systems but also enterprise environments where automated package management processes might be used, creating widespread potential for supply chain attacks. This weakness particularly impacts the security posture of Linux distributions that depend on third-party repositories for software installation, as it allows attackers to subvert the verification mechanisms designed to prevent unauthorized package modifications.
The vulnerability maps directly to CWE-295, which addresses "Improper Certificate Validation," and aligns with ATT&CK technique T1553.002 for "Subvert Trust Controls" and T1059.007 for "Command and Scripting Interpreter: Python." The attack vector requires network access to intercept traffic between the client and PPA servers, making it particularly relevant in environments where network traffic is not properly secured or where users connect to untrusted networks. Mitigation strategies include upgrading to software-properties version 0.81.13.3 or later, which implements proper certificate validation, and implementing network-level security controls such as SSL inspection and certificate pinning where appropriate. Organizations should also consider implementing additional verification mechanisms beyond simple GPG key checking, such as checksum validation of downloaded packages, and regular security audits of package repositories to detect potential compromise. The vulnerability demonstrates the critical importance of certificate validation in secure software distribution systems and serves as a reminder that even seemingly minor implementation flaws in security-critical components can have significant consequences for system integrity and user security.