CVE-2026-54576 in mport
Summary
by MITRE • 09/17/2026
mport is the MidnightBSD Package Manager. Prior to 2.7.8, do_actual_install() in libmport/bundle_read_install_pkg.c used path-based lstat(), chown(), stat(), and chmod() operations while installing package files. A local attacker with write access to a target directory could replace a checked file with a symlink before privileged ownership or mode changes were applied, redirecting those changes to an attacker-selected path and compromising filesystem integrity or permissions. This issue is fixed in version 2.7.8.
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Analysis
by VulDB Data Team • 09/18/2026
The MidnightBSD Package Manager, known as import, serves as the primary tool for managing software packages on the Midnight BSD operating system. In versions prior to 2.7.8, a critical security flaw existed within the package installation logic, specifically in the do_actual_install function located in libmport/bundle_read_install_pkg.c. This vulnerability stems from a classic Time-of-Check to Time-of-Use race condition combined with improper handling of symbolic links during file system operations. The core issue arises because the software performs security checks on files based on their path names but subsequently applies privileged ownership and permission changes using those same paths without verifying that the underlying inode remains unchanged or is not a symlink.
The technical flaw manifests when an attacker who possesses write access to a target directory where packages are being installed can manipulate the file system state between the initial check and the application of privileges. Specifically, after the package manager verifies the integrity or existence of a file but before it executes chown, chmod, stat, or lstat operations with elevated permissions, the attacker replaces the original checked file with a symbolic link pointing to an arbitrary location on the file system. Because the subsequent privileged commands operate directly on the path provided rather than validating the inode identity, they follow the symlink and apply ownership or permission changes to the target of the link chosen by the attacker. This behavior bypasses standard security controls that rely on path-based validation without atomicity guarantees.
The operational impact of this vulnerability is significant for system integrity and access control. By exploiting this flaw, a local user with limited privileges can escalate their influence over critical system files or directories outside their intended scope. For instance, an attacker could redirect chmod operations to modify permissions on sensitive configuration files or binaries owned by root, potentially enabling further exploitation vectors such as privilege escalation via setuid bits or unauthorized access to restricted resources. Similarly, chown redirections allow the attacker to take ownership of arbitrary system objects, which can be leveraged for persistence mechanisms or denial-of-service attacks against critical services. This compromises the fundamental trust model of the operating system by allowing unprivileged users to alter security-critical attributes of files they do not own and were never intended to modify.
This vulnerability aligns with Common Weakness Enumeration CWE-59, which describes Improper Link Resolution Before File Access, often referred to as a symbolic link following attack. It also relates closely to CWE-367, Time-of-check Time-of-use Race Condition, as the security check and the privileged action are not performed atomically. From an adversary perspective, this technique is consistent with ATT&CK tactic T1548, specifically subtechnique T1548.002 for Abuse Elevation Control Mechanism, where attackers manipulate system configurations to bypass access controls. The exploitation requires local physical or remote shell access and write permissions in the installation directory, limiting its scope but making it a potent threat in multi-user environments or shared hosting scenarios.
To mitigate this vulnerability, administrators must upgrade the MidnightBSD Package Manager to version 2.7.8 or later, where the code has been patched to resolve these race conditions and symlink handling issues. The fix likely involves using atomic operations such as open with O_NOFOLLOW flags for file descriptor acquisition before applying permissions, ensuring that symbolic links are either rejected or handled safely without following them into privileged contexts. Additionally, system administrators should enforce strict directory permissions on package installation targets to prevent unauthorized users from creating symlinks in those locations. Implementing mandatory access control policies and regularly auditing file ownership changes can provide additional layers of defense against similar exploitation attempts in legacy systems that cannot be immediately upgraded.