CVE-2026-96276: Flatpak: flatpak: arbitrary write in host context via flatpak build-init
If a malicious SDK container declares an extension point with a crafted directory path, and a developer runs flatpak build-init --writable-sdk --sdk-extension with that SDK, attacker-chosen files could be written outside the working directory, since the target path is resolved via a function that allows .. traversal.
Affected Software
Event History
Frequently Asked Questions
Who is exposed to this issue?
Developers who run flatpak build-init with both --writable-sdk and --sdk-extension against a malicious SDK container are exposed. The impact is an arbitrary file write in the host context outside the intended working directory.
What does an attacker need to exploit it?
An attacker needs to provide or induce use of an SDK container that declares an extension point with a crafted directory path. Exploitation also requires the developer to invoke flatpak build-init with --writable-sdk and --sdk-extension using that SDK.
Is a normal flatpak build-init invocation affected?
The described condition specifically requires use of both --writable-sdk and --sdk-extension. The available information does not indicate that invocations without those options are affected.
What can be done before a fix is available?
Do not use untrusted SDK containers with flatpak build-init when enabling --writable-sdk and --sdk-extension. Restrict SDK sources to trusted containers until the issue is remediated.