Symlink-based arbitrary file write in Flatpak ld cache regeneration (fixed in 1.18.1)
Flatpak versions before 1.18.1 follow attacker-controlled symlinks when regenerating the dynamic linker cache for a sandboxed app: a malicious app can replace ~/.var/app/$appid/.ld.so with a symlink, causing Flatpak's regenerate_ld_cache routine to write its cache files at an arbitrary filesystem location. The write happens through normal app-launch/cache-regeneration flows, so no privileges or user interaction are required beyond the malicious app already being installed and run. What the attacker gains is limited: the filename and contents of the written files are not attacker-controlled, which the CVE description itself notes makes the flaw hard to exploit, so realistic impact is low integrity/availability impact (file clobbering or corruption) rather than straightforward code execution. Anyone running Flatpak before 1.18.1 on a Linux desktop with sandboxed apps installed is theoretically in scope, though exploitation depends on having a malicious app in place. No public proof-of-concept is known, this is not on the CISA KEV list, and no exploitation in the wild has been reported.
What to do: Upgrade Flatpak to 1.18.1 or later (or apply your distribution's backported security update) — the release notes indicate 1.18.1 fixes multiple vulnerabilities, so it is worth prioritizing. Verify with 'flatpak --version' on Linux desktops under management. Additionally, audit installed Flatpak apps and their remotes for untrusted sources, and check ~/.var/app/<appid>/.ld.so paths for unexpected symlinks, removing any found.
| Flatpak (freedesktop.org) Flatpak | before 1.18.1 (all versions prior to 1.18.1; note distributions may ship backported fixes in older version branches) |
In Flatpak before 1.18.1, a malicious sandboxed app can replace ~/.var/app/$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.
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
MITRE assigned CVE-2026-96808 and CVE-2026-96807 to Flatpak flaws fixed in 1.18.1.
Simon McVittie reported on oss-security that MITRE assigned CVE identifiers for two Flatpak issues fixed in version 1.18.1. CVE-2026-96808 corresponds to GHSA-qrwq-7qwx-q9rp, and CVE-2026-96807 corresponds to GHSA-99wv-m8rp-g58x. The note does not describe impact or exploitation.