Executive brief
A flaw in the uutils coreutils library causes several common file management tools (cp, mv, install, and ln) to fail to create backup files when the --suffix option is used by itself. This behavior differs from the standard GNU tools that users expect, leading to situations where existing files are overwritten without a backup being created. This can result in the permanent loss of important data for users or automated scripts that rely on these backups for safety.
Technical details
The vulnerability exists in the `determine_backup_mode` function within `src/uucore/src/lib/features/backup_control.rs`. The logic incorrectly returns `BackupMode::None` if only the `--suffix` flag is provided, failing to trigger the backup mechanism. In standard GNU coreutils, the presence of `--suffix` alone is sufficient to enable backup mode. This affects the `cp`, `install`, `mv`, and `ln` utilities. An attacker or a routine operation could result in unintended file overwrites (Integrity loss) because the expected backup file is never created. The issue was resolved in uucore version 0.6.0 by updating the logic to resolve the backup mode from the `$VERSION_CONTROL` environment variable when `--suffix` is present.
Affected products
- uutils uucore < 0.6.0
- uutils coreutils < 0.6.0
Timeline
- 2025-12-21: patched: Fixed in PR #9741 and merged into main branch
- 2026-01-20: disclosed: Reported by Zellic in security assessment for Canonical
- 2026-05-31: advisory: GitHub Advisory published