Sparkle, a macOS software update framework, has a path‑traversal vulnerability in its binary delta application. The framework rejects writes whose immediate parent directory is a symbolic link, but fails to detect symbolic links that appear deeper in the relative path. During extraction, it creates symlinks in the destination without checking the symlink target, and a later extraction targeting a file under such a symlink (for example, '<symlink>/foo/bar') allows the system call to open a path resolved outside the intended directory, enabling arbitrary file writes. Exploitation requires a malicious .delta file that passes EdDSA signature verification, i.e. a compromised private key. If AppInstaller runs as root for system‑domain installs, the flaw allows the attacker to write any file at the root level, providing privilege escalation beyond the normal drop‑in replacement bundle. The issue is fixed in version 2.9.2.

The Sparkle framework produced by the Sparkle Project for macOS versions earlier than 2.9.2 is affected.

The CVSS score of 6.1 indicates moderate severity, while the EPSS score of less than 1% suggests a very low likelihood of exploitation at present. The vulnerability is not listed in the CISA KEV catalog. Exploitation requires a stolen EdDSA private key and a local update context, so the risk is moderate under normal conditions but could be severe for installations that run AppInstaller as root for system‑domain updates, providing arbitrary root‑level file writes.