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CVE-2024-27297 represents a severe security vulnerability within the Nix package manager and multi-user NixOS environments where unprivileged users can submit custom builds to the central Nix daemon. During the compilation and output registration phase of fixed-output derivations, Nix creates temporary `.tmp` directories inside the build chroot to stage build artifacts before moving them to the immutable Nix store. A critical architectural flaw arises because the orchestration process running in the host mount namespace improperly handles symbolic links created during this staging process. When the final output registration occurs, the high-privilege Nix daemon follows these user-controlled symbolic links located at the target destination path. Because the daemon executes with root permissions in multi-user installations, following a carefully crafted symlink allows an attacker to redirect file write operations away from the intended store path and directly onto arbitrary sensitive files on the underlying host filesystem. An attacker with local build privileges can leverage this race condition or deterministic file replacement to overwrite critical system configuration files, replace system binaries, or plant malicious executables that execute automatically with root privileges. In environments utilizing automated agent configurations or continuous integration pipelines without strict sandbox isolation and safety gates, this vulnerability enables complete system takeover. The vulnerability exposes the fundamental challenge of managing untrusted derivations, where isolated build processes interact with shared host-level orchestration routines. Remediating this issue requires updating the Nix package manager engine to ensure temporary output copy destinations are generated strictly within secure, unguessable internal store paths inaccessible to unprivileged users, while simultaneously hardening daemon configuration settings, restricting allowed build users, and implementing real-time validation checks on all configuration deltas and package closures to prevent unauthorized system modifications and privilege escalation vectors across multi-user deployments.
DailyCVE Form:
Platform: NixOS package manager
Version: Before version 2.34
Vulnerability : Symlink following write
Severity: Critical
date: March 11 2024
Prediction: April 07 2024
What Undercode Say:
Analysis of the Nix daemon build orchestration logs reveals high susceptibility when untrusted users share access to multi-user builder nodes. Below are the diagnostic and auditing commands used to inspect store integrity and monitor derivation execution:
Verify Nix store database integrity and check contents nix-store --verify --check-contents --repair Scan system store closures and dependencies for known vulnerabilities vulnix --system --verbose Inspect specific fixed-output derivation logs for anomalous file operations nix log /nix/store/.drv
Exploit: (Educational Purposes!)
An attacker exploits CVE-2024-27297 by constructing a malicious fixed-output derivation that replaces the expected output staging directory with a symbolic link pointing to a critical system file on the host, such as `/etc/passwd` or an active service binary. When the unprivileged build finishes, the root-running Nix daemon attempts to copy the temporary build results to the registration target, blindly following the symlink. This forces the daemon to overwrite the host system file with arbitrary attacker-controlled data, resulting in immediate privilege escalation and arbitrary code execution as root.
Protection: from this CVE
Defense against this vulnerability requires immediate patching of the Nix package manager to versions where temporary staging directories are isolated inside secure, unguessable internal store paths. Administrators should restrict the `allowed-users` configuration parameter in `nix.conf` to trusted accounts only, disabling untrusted local build submissions. Additionally, implementing agent-driven safety gates and audit ledgers to monitor NixOS configuration deltas and cross-reference closures against vulnerability catalogs provides an essential layer of defense-in-depth against unauthorized modifications.
Impact:
Successful exploitation of CVE-2024-27297 leads to complete host compromise in multi-user NixOS installations. Attackers can achieve arbitrary file overwrites with root privileges, bypass sandbox isolation boundaries, escalate privileges from unprivileged accounts, manipulate system binaries, and establish persistent control over vulnerable infrastructure servers.
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Sources:
Reported By: github.com
Extra Source Hub:
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