## What does this PR do?
Closes a critical bypass of the dangerous-command approval system. The
normalizer that every command passes through before pattern matching
(`_normalize_command_for_detection`) already strips ANSI, null bytes,
fullwidth Unicode, backslash escapes and empty-quote token splits — but
it did nothing about the shell `IFS` variable. In any POSIX shell `$IFS`
and `${IFS}` expand to whitespace, so a command written as
`rm${IFS}-rf${IFS}/` is executed by the live shell as `rm -rf /` while
the detection regexes — which anchor on literal `\s` between a command and
its arguments — never fire.
The impact is severe: this evades BOTH layers at once. It slips past every
entry in `DANGEROUS_PATTERNS` (so `curl${IFS}...|sh`, `sed${IFS}-i`
against `~/.hermes/config.yaml`, sudo privilege flags, etc. auto-run with
no approval prompt) AND the unconditional hardline floor that is
documented as un-bypassable "not even with --yolo" (`rm -rf /`, `mkfs`,
`dd` to a raw block device, `shutdown`/`reboot`, fork bomb). A
prompt-injected or malicious instruction could wipe the host filesystem or
power the box off while the approval system reports nothing. Confirmed at
runtime before the fix: `detect_hardline_command('rm${IFS}-rf /')` returned
`(False, None)`.
The fix mirrors the shell's own expansion: it collapses `$IFS` / `${IFS}`
(including the bash substring form `${IFS:0:1}`) to a single space inside
the existing de-obfuscation block, so the whitespace-anchored patterns
match exactly as they do for the un-obfuscated command. It is deliberately
narrow and safe — a `\b` word boundary keeps it from touching unrelated
variables like `$IFSACONFIG`, so it cannot introduce false positives on
legitimate commands.
## Related Issue
N/A
## Type of Change
- [x] 🔒 Security fix
## Changes Made
- `tools/approval.py`: in `_normalize_command_for_detection`, substitute
`$IFS` / `${IFS}` (and `${IFS:...}`) expansions with a literal space
before dangerous/hardline pattern matching, alongside the existing
backslash and empty-quote de-obfuscation.
- `tests/tools/test_approval.py`: add `TestIFSWhitespaceBypass` covering
the brace, bare and substring IFS forms against both
`detect_hardline_command` and `detect_dangerous_command`, plus
regression guards that a look-alike variable (`$IFSACONFIG`) and plain
safe commands are not flagged. Import `detect_hardline_command`.
## How to Test
1. Reproduce the hole (pre-fix): `detect_hardline_command('rm${IFS}-rf /')`
returns `(False, None)` and `detect_dangerous_command(...)` returns
`(False, ...)`, i.e. a host-destroying command is auto-approved.
2. With the fix applied, both now flag the command: hardline match
"recursive delete of root filesystem" and dangerous match "delete in
root path".
3. Run the suite: `pytest tests/tools/test_approval.py
tests/tools/test_hardline_blocklist.py -q` — the new
`TestIFSWhitespaceBypass` cases pass and nothing else regresses.
## Checklist
### Code
- [x] I've read the Contributing Guide
- [x] My commit messages follow Conventional Commits (`fix(scope):`, etc.)
- [x] I searched for existing PRs to make sure this isn't a duplicate
- [x] My PR contains **only** changes related to this fix (no unrelated commits)
- [x] I've run the relevant tests and they pass (two pre-existing failures
are environmental: missing optional deps in the minimal venv, not
caused by this change)
- [x] I've added tests for my changes
- [x] I've tested on my platform: macOS 15 (Darwin 25.5)
### Documentation & Housekeeping
- [x] I've updated relevant documentation (README, `docs/`, docstrings) — or N/A
- [x] I've updated `cli-config.yaml.example` if I added/changed config keys — or N/A
- [x] I've updated `CONTRIBUTING.md` or `AGENTS.md` if I changed architecture or workflows — or N/A
- [x] I've considered cross-platform impact (Windows, macOS) — the change is a
pure string transform with no platform-specific behavior; footgun gate passes
- [x] I've updated tool descriptions/schemas if I changed tool behavior — or N/A
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