CVE-2026-126074

### Impact `ActiveStorage::Filename#base` and `#extension_with_delimiter`, and therefore `#extension`, pass the stored filename unmodified to `File.basename` and `File.extname`, which raise `ArgumentError` when the name contains a NUL byte. Active Storage stores the client-supplied filename verbatim, so a user who is permitted to upload an attachment could persist such a filename on databases that accept NUL bytes in string columns, such as SQLite and MySQL/MariaDB. Each subsequent request that builds a variant or preview of the blob, opens it, or renders it as an Action Text attachment then raises, possibly resulting in a persistent DoS vulnerability for the pages that display the blob until it is purged or its filename is corrected. Applications that use PostgreSQL are not affected, because PostgreSQL rejects the row. ### Details `Filename#base` and `#extension_with_delimiter` now derive from `Filename#sanitized`, the form that `Filename#to_s` and the `Content-Disposition` header already use. For a filename that `#sanitized` changes, such as one containing a NUL byte, an invalid byte sequence, a path separator or another replaced character, the base and extension now agree with `#to_s`; the variant format inferred from such a name may change, and an existing variant may be regenerated once. Stored filenames are not modified, and no data migration is required. ### Releases The fixed releases are available at the normal locations. Patches for those who cannot upgrade at once: - 8.1: https://github.com/rails/rails/commit/60f22af88b71eae251f112d8c0237a08a8832692.patch - 8.0: https://github.com/rails/rails/commit/9b0d4bef2211a2c08cab2e0ea17fa1d0efd5d47a.patch ### Credit This issue was found by the Anthropic OSS Scanner (ANT-2026-UQM5Z4YL).