CVE-2026-96276 in Red Hat
Summary
by MITRE • 09/23/2026
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.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability described involves a critical path traversal flaw within Flatpak's build initialization process, specifically when handling software development kit extensions. This issue arises from an insufficient validation of user-supplied input in the form of extension point configurations declared by malicious SDK containers. When a developer utilizes the flatpak build-init command with the writable-sdk and sdk-extension flags, the system attempts to resolve file paths for writing artifacts into the specified directory structure. However, the underlying function responsible for path resolution fails to adequately sanitize or restrict relative path components, particularly the parent directory traversal sequence represented by double dots. This oversight allows an attacker who controls the SDK container's extension point definition to manipulate the target destination of written files.
From a technical perspective, this is a classic example of CWE-22: Improper Limitation of a Pathname to a Restricted Directory, often referred to as path traversal or directory traversal. The core flaw lies in the application logic that processes the directory parameter without normalizing the input against absolute paths or stripping out relative navigation sequences before performing file system operations. By injecting ../ sequences into the declared extension point's directory field, an attacker can shift the write operation from the intended sandboxed working directory to arbitrary locations on the host filesystem where the developer is executing the build command. This bypasses the expected isolation boundaries that Flatpak aims to enforce during the development and packaging workflow.
The operational impact of this vulnerability is significant for developers relying on third-party SDK extensions. If successful, an attacker can write files outside the designated working directory, potentially overwriting critical system configuration files, injecting malicious scripts into executable paths, or compromising other sensitive data stored in accessible parent directories. This could lead to remote code execution if the written content includes executable payloads that are later invoked by the developer's environment or subsequent build processes. Furthermore, it undermines the integrity of the software supply chain, as trusted SDKs become vectors for arbitrary file writes, eroding trust in the package management ecosystem.
This vulnerability aligns with MITRE ATT&CK technique T1059: Command and Scripting Interpreter if the written files are scripts intended to be executed later, or more broadly with Supply Chain Compromise tactics where a trusted component is abused to gain unauthorized access. The lack of strict input validation on path parameters represents a fundamental security design flaw that violates principles of least privilege and secure defaults. Developers using affected versions must exercise extreme caution when integrating SDK extensions from untrusted sources until patches are applied.
Mitigation strategies primarily involve updating Flatpak to the latest stable version where this path traversal issue has been addressed through improved input sanitization and strict path normalization checks. Until such updates are available, developers should avoid using writable-sdk modes with sdk-extension flags unless they have thoroughly audited the source of the SDK container. Additionally, implementing file system access controls via SELinux or AppArmor profiles can provide an additional layer of defense by restricting write permissions to specific directories regardless of how paths are resolved within the application logic. Regular security audits of build scripts and dependency management processes are also recommended to detect any anomalous behavior indicative of such exploitation attempts.