GHSA-r4vp-3vw6-r2x5: Path Traversal

At a glance

- Actor: attacker who controls the -o/--output argument to trestle author {catalog,profile,ssp}-generate (e.g. via a CI pipeline that derives the output directory from repository-controlled data)

- Primitive: attacker-controlled --output value reaches trestleroot / args.output write sink with only isdirectorynameallowed() (parts[0]-only task-name-collision check), not the PathSecurityValidator.validatelocalpath() guard added by the CVE-2026-46345 fix

- Impact: arbitrary-location file write outside the trestle workspace as the process owner (8.4 High; conservative C:N variant 7.7, still High); with --force-overwrite, the attacker-chosen directory is first recursively deleted shutil.rmtree)

- Precondition: attacker influences the -o argument in a CI/automation pipeline or multi-tenant trestle workspace running these generate subcommands

- Fix: call PathSecurityValidator.validatelocalpath(markdownpath, trestleroot) immediately after building markdownpath in catalog.py, ssp.py, and prof.py, mirroring the existing jinja fix

Overview

The remediation for CVE-2026-46345 / GHSA-4q5v-7g7x-j79w ("Arbitrary File Write via Path Traversal in compliance-trestle – jinja") added a new PathSecurityValidator.validatelocalpath() guard and wired it into the jinja command's output path. The identical output = trestleroot / args.output write pattern in the sibling author commands — catalog-generate, profile-generate, and ssp-generate — was not updated. Those commands instead rely on isdirectorynameallowed(), a task-name-collision check that does not stop path traversal: an absolute --output or a --output whose first component is innocuous subdir/../../../...) escapes the trestle workspace and writes generated markdown under an attacker-chosen output root outside the workspace, subject to the invoking process's filesystem permissions.

Impact

Threat model. This is not a claim that a local user harms themselves by intentionally choosing an unsafe -o. The security boundary is crossed when a trusted automation job, CI workflow, shared trestle service, or wrapper invokes one of these subcommands and derives --output from repository-controlled, tenant-controlled, or otherwise untrusted data while expecting trestle to keep generated output inside the workspace. The attacker does not need local shell access to the trestle host; they only need influence over the data that the trusted automation maps into the --output argument.

Primary claim (confirmed): Such an invocation writes control-markdown files outside the trestle workspace — arbitrary-location file write as the process owner. This is runtime-confirmed for catalog-generate: catalog-generate -o /tmp/TRESTLEESCAPEABS produced files outside the workspace on a v4.0.3 install while the same install blocked the equivalent jinja -o with a Security violation error. profile-generate and ssp-generate are source-confirmed siblings (identical trestleroot / args.output join, the same isdirectorynameallowed-only gate, no validatelocalpath call); see Runtime-confirmed scope in the End-to-end verification below.

Destructive variant --force-overwrite, source-confirmed): before generating, the force-overwrite path clears the selected output directory via clearfolder(...) trestle/core/commands/common/cmdutils.py), which performs shutil.rmtree on that directory. Because clearfolder early-returns unless the target is an existing directory, the primitive is recursive deletion of an attacker-selected directory tree outside the workspace (e.g. wiping a directory the process owner can write), not pinpoint deletion of an arbitrary single file. This is the integrity + availability impact behind I:HA:H.

Secondary (conditional) escalation: The affected population extends to every consumer that runs these generate subcommands in a CI/automation pipeline, shared/multi-tenant trestle workspace, or wrapper that forwards an externally supplied name — the same threat model GitHub/the maintainer accepted for CVE-2026-46345. Indirect code execution (e.g. overwriting a script the CI pipeline later invokes) is the bounded escalation beyond the demonstrated file-write primitive.

Technical Details

Source → Transform → Sink → Missing-guard → Result: attacker-controlled --output CLI argument → trestleroot / args.output join in catalog.pyssp.pyprof.py → CatalogAPI.writecatalogasmarkdown() writes files under the resolved path → only isdirectorynameallowed() (parts[0]-only task-name check) applied, not PathSecurityValidator.validatelocalpath() → files written outside the trestle workspace.

The fix is scoped to jinja.py only

Both fix commits 247fcce2…, 7d107b3a…, "add path traversal protection and prevent SSTI in jinja templating") touch only trestle/core/commands/author/jinja.py (+ its tests). The new guard:

python trestle/core/commands/author/jinja.py outputfile = trestleroot / routputfile PathSecurityValidator.validatelocalpath(outputfile, trestleroot) # :229 (and :278, :297)

validatelocalpath trestle/core/remote/security.py:326) is the correct guard — it .resolve()s the path and calls relativeto(trestleroot), rejecting both .. traversal and absolute paths.

The sibling generate commands were not updated

catalog-generate, profile-generate, and ssp-generate build the output path with the same join but never call validatelocalpath. The only check is isdirectorynameallowed:

python trestle/core/commands/author/catalog.py:69 / ssp.py:97 / prof.py:86 (identical in all three) if not fileutils.isdirectorynameallowed(args.output): raise TrestleError(f'{args.output} is not an allowed directory name') ... markdownpath = trestleroot / args.output # catalog.py:90 / prof.py:110 (var markdownpath); ssp.py:111 (var mdpath) — same join

isdirectorynameallowed trestle/common/fileutils.py:95) was designed to stop task names that collide with OSCAL model directories, not traversal. It inspects only parts[0]:

python def isdirectorynameallowed(name: str) -> bool: pathedname = pathlib.Path(name) rootpath = pathedname.parts[0] if rootpath in const.MODELTYPETOMODELDIR.values(): return False # blocks "catalogs", "profiles", ... if rootpath[0] == '.': return False # blocks leading "." (i.e. "../x") if pathedname.suffix != '': return False # blocks names with a file suffix if 'global' in pathedname.parts: return False return True

Two payloads defeat it:

1. Absolute path — --output /tmp/pwned. parts[0] is / (not an OSCAL dir, not .-prefixed, no suffix) → allowed. trestleroot / '/tmp/pwned' collapses to /tmp/pwned (pathlib discards the left operand on absolute join).

2. Non-leading .. — --output subdir/../../../../../../tmp/pwned. parts[0] is subdir (innocuous) → allowed. The .. segments resolve out of the workspace at write time.

The validated value flows unchanged to the write sink with no further sanitisation grep for resolve()/relativeto/validatelocalpath across the catalog write path returns zero hits): ControlContext.generate(..., mdroot=markdownpath, ...) stores it as a dataclass field trestle/core/controlcontext.py:46) and CatalogAPI.writecatalogasmarkdown() calls self.context.mdroot.mkdir(existok=True, parents=True) trestle/core/catalog/catalogapi.py:72) then writes <control-id>.md files under it.

Additional unguarded siblings create, replicate)

trestle create trestle/core/commands/create.py:95, desiredmodeldir = trestleroot / pluralpath / args.output) and trestle replicate replicate.py:90) have no isdirectorynameallowed check at all and accept the same absolute / .. --output. They write a structured OSCAL model file and refuse to overwrite an existing target .exists() raises), so the primitive is create-only there — lower impact than the generate commands, but the same missing-guard root cause. These are flagged as related defense-in-depth sinks sharing the root cause, not as the primary impact claim of this report.

Severity note

Metrics mirror the parent CVE-2026-46345 (8.4, AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H). I:HA:H are direct and demonstrated: out-of-workspace file creation, plus recursive shutil.rmtree of an attacker-chosen directory under --force-overwrite. C:H is proposed for consistency with the parent advisory's published score for the same out-of-workspace write boundary; however, the directly demonstrated primitive is write/overwrite rather than file read, so a conservative vector with C:N AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H) yields 7.7, still High. S:U because trestle writes as the invoking user.

Why OSCAL id-validation does not prevent this

OSCAL model ids control.id, group.id) are NCName-validated constr(regex=…)) and cannot contain /, \, or a leading .., so the per-control leaf filenames grp1/ac-1.md) cannot themselves traverse. That validation does not help here: the base output root mdroot = trestleroot / args.output is built from the raw, unconstrained -o/--output CLI string and is joined before those safe leaves. An absolute or non-leading.. -o escapes the workspace, and the NCName-safe leaves are written underneath the escaped root — confirmed by the PoC, where the escape occurs at mdroot /tmp/TRESTLEESCAPEABS) with grp1/ac-1.md written beneath it.

Reproduction

Non-web target (Python CLI). PoC is a command sequence run against a local install of the project's current source (HEAD e22e35bd, reports as v4.0.3) — no vendor infrastructure touched.

Step 1 — Set up a normal trestle workspace with a one-control catalog

bash pip install -e . # editable install of the affected source (v4.0.3) mkdir /tmp/pocws && cd /tmp/pocws trestle init mkdir -p catalogs/mycat python3 - <<'PY' import uuid, json cat = {"catalog":{"uuid":str(uuid.uuid4()), "metadata":{"title":"PoC Catalog","last-modified":"2026-01-01T00:00:00.000+00:00","version":"1.0","oscal-version":"1.0.4"}, "groups":[{"id":"grp1","title":"Group One","controls":[ {"id":"ac-1","title":"PoC Control","parts":[{"id":"ac-1smt","name":"statement","prose":"PoC statement prose."}]}]}]}} json.dump(cat, open("catalogs/mycat/catalog.json","w"), indent=2) PY

Step 2 — Trigger the boundary failure (absolute-path escape)

bash trestle author catalog-generate -n mycat -o /tmp/TRESTLEESCAPEABS ls /tmp/TRESTLEESCAPEABS/grp1/ac-1.md

Recorded output:

text $ ls /tmp/TRESTLEESCAPEABS/grp1/ac-1.md /tmp/TRESTLEESCAPEABS/grp1/ac-1.md # written OUTSIDE /tmp/pocws $ head -3 /tmp/TRESTLEESCAPEABS/grp1/ac-1.md ac-1 - \[Group One\] PoC Control Control Statement

Step 3 — Same escape via non-leading .. (defeats isdirectorynameallowed)

bash trestle author catalog-generate -n mycat -o 'subdir/../../../../../../tmp/TRESTLEESCAPEDOTDOT' ls /tmp/TRESTLEESCAPEDOTDOT/grp1/ac-1.md # -> exists, outside the workspace

Step 4 — Differential: the patched jinja -o is blocked on the SAME install

bash echo 'hello {{ 1+1 }}' > template.j2 trestle author jinja -i template.j2 -o '/tmp/TRESTLEJINJABLOCKED'

Recorded output (fix is active; proves this is an incomplete fix, not an unpatched version):

text ERROR: ... Security violation: Path traversal blocked. Attempted to access "/tmp/TRESTLEJINJABLOCKED" which is outside the trestle workspace "/tmp/pocws" (no file created)

catalog-generate escapes while jinja is blocked → the validatelocalpath remediation was never applied to the generate commands.

End-to-end verification (runtime)

- Lab setup: editable install pip install -e .) of the affected source at HEAD e22e35bd (reports as v4.0.3, the release that contains the GHSA-4q5v jinja fix). import trestle.core.commands.author.catalog resolves to the in-tree source file, confirming the run exercises HEAD, not a stale wheel.

- Observed end-to-end effect (not an intermediate return value): files physically written outside the workspace — /tmp/TRESTLEESCAPEABS/grp1/ac-1.md and /tmp/TRESTLEESCAPEDOTDOT/grp1/ac-1.md — while /tmp/pocws (the trestle root) contained no such directory. Confirmed by findls.

- Differential control: the same install rejects the equivalent jinja -o with Security violation: Path traversal blocked … outside the trestle workspace, writing nothing. The guard exists and works in jinja; it is simply absent from the generate commands.

- Guard bypass, isolated: importing isdirectorynameallowed semantics and joining via pathlib confirms -o /tmp/pwned (absolute) and -o subdir/../../../tmp/pwned (innocuous leading component) both pass the check and resolve outside the root, while the naive -o ../../tmp/pwned is the only form the check stops.

- Runtime-confirmed scope (what was executed vs source-confirmed): the write escape is runtime-confirmed for catalog-generate (Steps 2–4 above). profile-generate and ssp-generate are source-confirmed siblings — same trestleroot / args.output join prof.py:110, ssp.py:111), same isdirectorynameallowed-only gate prof.py:86, ssp.py:97), no validatelocalpath — and should be fixed in the same patch. The --force-overwrite recursive-delete primitive clearfolder → shutil.rmtree, with an early return unless the target is an existing directory) is source-confirmed; the PoC above exercises the write escape, not -fo.

Suggested Fix

Root-cause fix: Mirror the jinja fix in the three generate commands (and, for completeness, createreplicate): after constructing the output path, call the existing guard before any mkdir/write.

python catalog.py / ssp.py / prof.py, immediately after markdownpath = trestleroot / args.output from trestle.core.remote.security import PathSecurityValidator PathSecurityValidator.validatelocalpath(markdownpath, trestleroot)

isdirectorynameallowed() should be retained for its original purpose (OSCAL-dir-collision prevention) but must not be relied on for traversal defence.

Defense-in-depth: Harden isdirectorynameallowed to reject absolute paths pathedname.isabsolute()) and any .. component so it provides a secondary layer even if the primary validatelocalpath call is accidentally omitted in future.

References

- Vendor security policy: https://github.com/oscal-compass/compliance-trestle/security/policy

- Submission endpoint: https://github.com/oscal-compass/compliance-trestle/security/advisories/new

- Parent advisory (incompletely fixed): GHSA-4q5v-7g7x-j79w / CVE-2026-46345 — "Arbitrary File Write via Path Traversal in compliance-trestle – jinja"

- Coordinated disclosure batch (part of the same PathSecurityValidator remediation): GHSA-gg2g-p7xc-qqmm (SSTI RCE), GHSA-g3vg-vx23-3858 (cache path traversal), GHSA-mj4x-vf5c-5xg8 (profile-import path traversal read), GHSA-w76h-q7c6-jpjp (SSRF)

- Fix commits (jinja-only scope): 247fcce289f60103f3d8e28d8ec51a6986b94fb6, 7d107b3ac53caca7bde97a6278b23cd739d94525

- Affected sinks: trestle/core/commands/author/catalog.py:69,90; author/ssp.py:97,111; author/prof.py:86,110; bypassed guard trestle/common/fileutils.py:95; write sink trestle/core/catalog/catalogapi.py:72; unused-here correct guard trestle/core/remote/security.py:326

- Additional unguarded siblings: trestle/core/commands/create.py:95, trestle/core/commands/replicate.py:90