CVE-2017-9269 in libzypp
Summary
by MITRE
In libzypp before August 2018 GPG keys attached to YUM repositories were not correctly pinned, allowing malicious repository mirrors to silently downgrade to unsigned repositories with potential malicious content.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability described in CVE-2017-9269 represents a critical flaw in the libzypp package management library that affected systems using YUM-based repositories. This issue specifically pertained to the improper handling of GPG key pinning mechanisms within the package management infrastructure. The flaw allowed attackers to exploit repository mirroring configurations in a manner that could silently downgrade legitimate signed repositories to unsigned counterparts without proper validation. The vulnerability existed in libzypp versions released prior to August 2018, creating a window of opportunity for malicious actors to manipulate package installation processes.
The technical root cause of this vulnerability lies in the insufficient validation of GPG key signatures when repository mirrors were being utilized. When systems retrieved packages from YUM repositories, the libzypp library failed to maintain strict pinning of the original GPG keys associated with trusted repositories. This weakness enabled attackers who controlled malicious repository mirrors to present unsigned packages or packages signed with compromised keys while maintaining the appearance of legitimate repository operations. The flaw essentially allowed for a form of repository poisoning that could occur without detection, as the system would continue to operate under the assumption that it was receiving authenticated content.
From an operational impact perspective, this vulnerability created significant security risks for enterprise environments relying on YUM-based package management systems. Systems could be silently compromised through package installation processes, potentially allowing attackers to install malicious software alongside legitimate updates. The silent nature of the downgrade meant that administrators would not receive alerts or notifications about the repository switch, making detection particularly challenging. Organizations using automated deployment systems or continuous integration pipelines were especially vulnerable, as these environments often rely heavily on package repositories and may not manually verify repository integrity.
The vulnerability aligns with CWE-295 which addresses improper certificate validation and can be mapped to ATT&CK technique T1059.001 for execution through package management systems. This flaw demonstrates how repository management configurations can be exploited to bypass security controls that should prevent unauthorized package installation. The attack vector specifically targets the trust model of package management systems, where repository authenticity is assumed rather than rigorously validated. Organizations implementing security controls around package management should consider this vulnerability when establishing repository trust policies and monitoring for unauthorized repository modifications.
Effective mitigations for CVE-2017-9269 require immediate patching of libzypp to versions released after August 2018, which addressed the GPG key pinning implementation. System administrators should also implement repository integrity monitoring to detect unauthorized changes to repository configurations. Additional protective measures include enabling strict GPG signature verification for all package installations, implementing repository whitelisting policies, and conducting regular audits of repository configurations. Organizations should also consider implementing network-level controls to prevent access to untrusted repository mirrors and establish automated alerting for repository configuration changes. The vulnerability underscores the importance of maintaining current package management software versions and implementing comprehensive repository security policies that go beyond simple trust assumptions.