The GNU Guix project has announced three vulnerabilities in the guix substitute utility as well as a fourth that affects the guix pull and guix time-machine commands. The impact of the vulnerabilities ranges from remote privilege escalation to local disclosure of sensitive files.

The remote exploitation of guix substitute only requires that the vulnerable system attempt to download a binary substitute. Any configured substitute server, including ones discovered using guix-daemon's --discover option, can exploit this, and so can a man-in-the-middle (MITM), regardless of whether https is used in the substitute server urls.

The local exploitation of guix substitute only requires the ability to connect to guix-daemon's socket, which by default any user can do.

Separately, another security issue (CVE ID pending) was identified in guix pull and guix time-machine, which enables anyone who can control the channels file used by these commands to cause a file to be created or overwritten wherever the user running the command in question has permission to create them.

The project is recommending that all users upgrade guix and guix-daemon immediately. See the announcement for instructions, how to test for the vulnerabilities, the disclosure timeline, and more.

A number of problems related to negative directory entries (dentries) were the topic of a filesystem-track session at the 2026 Linux Storage, Filesystem, Memory Management, and BPF Summit. Negative dentries are used to indicate that a file of a given name does not exist in a directory; it is an optimization that short-circuits the lookup of the file name when the answer is already known. Miklos Szeredi led a session that discussed some problems that come from having too many negative dentries for a directory.

Security updates have been issued by AlmaLinux (389-ds-base, bind9.18, evince, fence-agents, freerdp, frr, frr10, gimp, gnutls, hplip, jmc, mariadb:11.8, mysql:8.4, php:7.4, postgresql-jdbc, postgresql:15, postgresql:16, valkey, xorg-x11-server, and xorg-x11-server-Xwayland), Debian (fastnetmon), Fedora (7zip, apptainer, cpp-httplib, mysql8.4, and nmap), Oracle (freerdp, giflib, glib2, glibc, kernel, libreoffice, libvirt, mariadb:10.11, postgresql, python3.11, python3.12, rrdtool, and thunderbird), Red Hat (buildah, podman, and skopeo), SUSE (alloy, apache2, buildah, c3p0, containerd, crun, cups, dhcpcd, dnsmasq, docker-stable, dracut, editorconfig-core-c, ffmpeg-7, fontforge, google-guest-agent, google-osconfig-agent, graphicsmagick, gstreamer-plugins-bad, gstreamer-plugins-good, helm, jackson-annotations, jackson-core, jackson-databind, jline3, kernel, kubectl-cnpg, lcms2, libslirp, libssh2_org, libxreaderdocument3, openbabel, openssl-3, pacemaker, perl-CGI-Session, perl-list-someutils-xs, python-lxml, python-tornado, python-tornado6, python3-onionshare, python311-python-engineio, sg3_utils, thunderbird, transmission, and trivy), and Ubuntu (cifs-utils, kernel, libvncserver, linux-aws-6.8, linux-gcp-6.8, linux-gke, linux-gkeop, linux-ibm-6.8, linux-nvidia-lowlatency, linux-oracle-6.8, linux-lowlatency, linux-lowlatency-hwe-6.8, linux-nvidia-tegra, linux-oracle-5.15, linux-raspi, linux-xilinx, nghttp2, nginx, perl, and vim).