GHSA-69qj-pvh9-c5wg

### Summary yt-dlp's `--exec` option is vulnerable to arbitrary command injection when handling untrusted metadata if the argument uses standard string formatting (e.g. `%(title)s`) or other unsafe conversions. An attacker could achieve remote code execution on the user's machine via maliciously crafted metadata containing quotes or other special shell characters. ### Details Since yt-dlp version 2021.04.11, the `--exec` option has supported "output template syntax", which is a superset of Python's `printf`-style string formatting also used by the `--output` option. This means the user is able to pass a "command template" as an argument to the `--exec` option which will be executed by the user's shell. The command template allows for the downloaded video's metadata to be interpolated into the command string. yt-dlp implements a `%()q` conversion, which will shell-quote/escape any metadata value such that it is safe to be interpolated into a command string. However, there are unsafe conversions such as `%()s` which result in the command template being formatted with the raw metadata string. These unsafe conversions do not perform any sanitization or escaping for shell contexts. If one or more of these unsafe conversions is used in the command template, an attacker can craft a malicious metadata value containing shell operators (e.g. `;`, `&`, `|`) to break out of the intended command and execute payload commands. ### Impact The impact is limited to users who pass an `--exec` command template containing unsafe conversions in their yt-dlp command or configuration file: `%()s`, `%()a`, `%()r`, `%()j`, `%()S` (including any of their flagged variants.) ### Patches yt-dlp version 2026.06.09 fixes this issue by restricting the conversions that can be used in an `--exec` command template to those known to be safe: `%()d`, `%()i`, `%()f`, `%()q` (including any of their flagged variants.) It also restricts the characters that can be used in command template defaults and