CVE-2026-96807

In Flatpak before 1.18.1, a malicious sandboxed app can replace ~/.var/app/$appid/.ld.so with a symlink, causing regenerate_ld_cache to write files at an arbitrary location. The filenames and content are not attacker controlled, making this hard to exploit.

• CVE-2026-96807: regenerate_ld_cache() created and bind-mounted the per-app .ld.so directory by path, and flatpak_switch_symlink_and_remove() swapped its "active" symlink with path-based symlink()/rename()/unlink(), so a sandboxed app could replace ~/.var/app/$APPID/.ld.so with a symlink and have ld.so cache files written at an arbitrary host location; regenerate_ld_cache() now opens the directory with glnx_chase_and_mkdirat(), works on it with *at() syscalls and passes it to bwrap with --bind-fd, and flatpak_switch_symlink_and_remove() takes the directory fd and uses symlinkat()/renameat()/unlinkat()
• Fix flatpak_switch_symlink_and_remove() returning -1 (truthy) instead of FALSE on one error path

• CVE-2026-96807: harden regenerate_ld_cache and flatpak_switch_symlink_and_remove against .ld.so symlink attacks by using fd-based operations and bwrap --bind-fd

This update for flatpak fixes the following issues:

• CVE-2026-90616: missing symlink protection allows a malicious sandboxed app to obtain arbitrary read and write access to files on the host (bsc#1280236).
• CVE-2026-92162: path traversal via unvalidated arch parameter in DeployAppstream (bsc#1282514).
• CVE-2026-96275: arbitrary write access as root via extra-data extraction (bsc#1282515).
• CVE-2026-96276: arbitrary write in host context via flatpak build-init (bsc#1282516).
• CVE-2026-96281: unprivileged active user can bypass anti-downgrade checks for system apps/runtimes (bsc#1282519).
• CVE-2026-96282: extension metadata path traversal file existence oracle (bsc#1282520).
• CVE-2026-96283: flatpak-system-helper: cross-user CancelPull orphans another user's ongoing pull (bsc#1282521).
• CVE-2026-96807: fixed-filename writes to arbitrary locations via symlink attack on .ld.so (bsc#1282523).
• CVE-2026-96808: revokefs symlink path traversal allows local privilege escalation via commit tampering (bsc#1282524).

This update for flatpak fixes the following issues:

• CVE-2026-90616: missing symlink protection allows a malicious sandboxed app to obtain arbitrary read and write access to files on the host (bsc#1280236).
• CVE-2026-92162: path traversal via unvalidated arch parameter in DeployAppstream (bsc#1282514).
• CVE-2026-96275: arbitrary write access as root via extra-data extraction (bsc#1282515).
• CVE-2026-96276: arbitrary write in host context via flatpak build-init (bsc#1282516).
• CVE-2026-96280: buffer overflow in OCI delta stream path names (bsc#1282518).
• CVE-2026-96281: unprivileged active user can bypass anti-downgrade checks for system apps/runtimes (bsc#1282519).
• CVE-2026-96282: extension metadata path traversal file existence oracle (bsc#1282520).
• CVE-2026-96807: fixed-filename writes to arbitrary locations via symlink attack on .ld.so (bsc#1282523).
• CVE-2026-96808: revokefs symlink path traversal allows local privilege escalation via commit tampering (bsc#1282524).

Changes for flatpak:

• Update to version 1.16.6 (jsc#PED-17048):

• Fix file descriptor leaks affecting Chromium-based browsers.
• Fix installing extra-data without a runtime, including openh264.
• Fix unusable sandbox-expose paths affecting Epiphany.
• Fix installed tests and handling of file descriptor arguments.

• Changes from version 1.16.5:

• Fix regressions from the sandbox escape security fix affecting browsers, browser-based apps and Steam.
• Expand test coverage of flatpak-run features used by the portal.

• Changes from version 1.16.4:

• Prevent arbitrary file reads in the system-helper context (GHSA-2fxp-43j9-pwvc).
• Prevent orphaning cross-user pull operations (GHSA-89xm-3m96-w3jg).

• Changes from version 1.16.3:

• Be selective about mapping font-dirs.xml in flatpak build.

• Changes from version 1.16.2:

• Support reinstalling bundle installations and Intel Xe VA-API.
• Add cancellation support for curl downloads.
• Fix font configuration, mask and pin configuration reloads, unintended home directory access, flatpak kill, OCI support, memory leaks and crashes.

• Changes from version 1.16.1:

• Allow updating existing apps under parental controls by default.
• Use instance IDs for systemd scopes and include /dev/udmabuf with --device=dri.
• Speed up prune --dry-run and permission-reset.
• Support TLS certificates in /etc/containers/certs.d for OCI.
• Fix portal crashes, sandbox environment handling, accessibility bus discovery, error reporting and shell completion.
• Update documentation and translations.

This update for flatpak fixes the following issues:

• CVE-2026-34078: Arbitrary code execution via crafted symlinks in sandbox-expose options (bsc#1261769).
• CVE-2026-34079: Arbitrary file deletion on host via improper cache file path validation (bsc#1261770).
• CVE-2026-90616: missing symlink protection allows a malicious sandboxed app to obtain arbitrary read and write access to files on the host (bsc#1280236).
• CVE-2026-92162: path traversal via unvalidated arch parameter in DeployAppstream (bsc#1282514).
• CVE-2026-96275: arbitrary write access as root via extra-data extraction (bsc#1282515).
• CVE-2026-96276: arbitrary write in host context via flatpak build-init (bsc#1282516).
• CVE-2026-96280: buffer overflow in OCI delta stream path names (bsc#1282518).
• CVE-2026-96281: unprivileged active user can bypass anti-downgrade checks for system apps/runtimes (bsc#1282519).
• CVE-2026-96282: extension metadata path traversal file existence oracle (bsc#1282520).
• CVE-2026-96807: fixed-filename writes to arbitrary locations via symlink attack on .ld.so (bsc#1282523).
• CVE-2026-96808: revokefs symlink path traversal allows local privilege escalation via commit tampering (bsc#1282524).

Changes for flatpak:

• Update to version 1.16.6 (jsc#PED-17048):

• Fix file descriptor leaks affecting Chromium-based browsers.
• Fix installing extra-data without a runtime, including OpenH264.
• Ignore unusable sandbox-expose paths for portal sub-sandboxes, fixing Epiphany regressions.
• Fix installed tests and handling of standard file descriptors passed as invalid flatpak run arguments.

• Switch from Autotools to Meson, preserving system bubblewrap, xdg-dbus-proxy, curl and distribution-specific installation paths.
• Require bubblewrap >= 0.10.0 and GPGME >= 1.8.0; add Meson, gettext, gtk-doc and polkit-agent build dependencies and drop obsolete intltool and libelf build dependencies.
• Generate the system-user pre-script from the Meson build directory and package the tmpfiles configuration and renamed manual pages.