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CVE-2026-90616

• Severity: high (CVSS 7.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-12 · updated 2026-09-22
• Weakness: CWE-61

Description

In Flatpak before 1.18.1, a malicious sandboxed app can obtain arbitrary read and write access to files on the host, which can be escalated to arbitrary code execution on the host, a different vulnerability than CVE-2026-76925. Flatpak creates a few app data directories (e.g., /var/cache, /var/data, /var/config, and /var/tmp) in every sandbox on every app launch where, in some cases, components of the path are attacker-controlled. Missing symlink protection can redirect the directories. Some of these directories are bind-mounted by Flatpak by passing the path (e.g., /home/user/.var/app/APP_ID/cache/tmp), which contains attacker-controlled directories (tmp) to bwrap --bind SRC DST. bwrap passes the path on to the kernel, which then follows symlinks. A malicious symlink can point to arbitrary locations on the host and it will become mounted inside the sandbox.

Affected products

• flatpak: before 1.18.1 — fixed in 1.18.1

How to fix

Upgrade to a fixed version: flatpak 1.18.1. Check the vendor advisory for mitigations.

References

• https://github.com/flatpak/flatpak/security/advisories/GHSA-8688-9x26-hhxj
• https://www.openwall.com/lists/oss-security/2026/08/11/9

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