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fix(sandbox): resolve symlinks before the read-path containment check - #49
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…eadFile Use fs.realpath() to resolve symlinks before checking whether the path falls within allowed roots, and pass the resolved path to readFile(). This prevents symlink-based path traversal (CWE-22) where a symlink inside an allowed root points to a file outside it.
Reviewer's GuideFixes CWE-22 in sandboxed fs.readFile by preserving the fast lexical check, resolving both requested paths and configured roots before containment validation, and reading only the validated real path; adds temporary-directory tests covering normal reads, symlink escapes, early rejection, and symlinked roots. Sequence diagram for symlink-safe sandboxed file readssequenceDiagram
participant Code as Sandboxed code
participant Forge as SandboxedToolForge
participant FS as fs/promises
Code->>Forge: fs.readFile(filePath)
Forge->>Forge: path.resolve(filePath)
alt Outside configured lexical roots
Forge-->>Code: throw blocked error
else Within lexical roots
Forge->>FS: realpath(resolvedPath)
FS-->>Forge: realPath
Forge->>Forge: resolveReadRoots()
Forge->>FS: realpath(configured roots)
FS-->>Forge: real roots
alt realPath outside real roots
Forge-->>Code: throw blocked error
else Within real roots
Forge->>FS: readFile(realPath)
FS-->>Forge: file data
Forge-->>Code: return data
end
end
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ChangesSymlink-aware filesystem containment
Priority: ⬆️ High Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix Merge Risk: ⚪ Minimal · up to The symlink containment changes are merge-ready; no supported issue remains in the reviewed paths. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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PR Summary by QodoHarden sandbox reads against symlink path escapes
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Hey - I've found 1 issue
Prompt for AI Agents
Please address the comments from this code review:
## Individual Comments
### Comment 1
<location path="src/cognition/emergent/SandboxedToolForge.ts" line_range="507-508" />
<code_context>
- return resolvedPath === root || resolvedPath.startsWith(`${root}${path.sep}`);
- });
- if (!allowed) {
+ const withinRoots = (candidate: string, roots: readonly string[]): boolean =>
+ roots.some((root) => candidate === root || candidate.startsWith(`${root}${path.sep}`));
+
+ // Lexical pass: rejects the obvious `../../etc/passwd` shape before
</code_context>
<issue_to_address>
**issue (bug_risk):** withinRoots rejects every descendant of a filesystem-root allowlist such as `/` because it checks for a prefix of `//`; consequently configuring `fsReadRoots: ['/']` blocks valid reads such as `/etc/hosts`. The same failure occurs for a Windows drive root such as `C:\`, where the constructed prefix is `C:\\`.
**Triggers:** When an allowed root is the filesystem root or a Windows drive root.
**Suggested fix:** Use `path.relative` to determine containment, or special-case filesystem roots before appending `path.sep`.
```suggestion
const withinRoots = (candidate: string, roots: readonly string[]): boolean =>
roots.some((root) => {
const relative = path.relative(root, candidate);
return (
relative === '' ||
(relative !== '..' &&
!relative.startsWith(`..${path.sep}`) &&
!path.isAbsolute(relative))
);
});
```
</issue_to_address>
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- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
In `@src/cognition/emergent/SandboxedToolForge.ts`:
- Around line 507-508: Update the withinRoots containment check to use
path.relative() instead of string equality and startsWith comparisons. Treat an
empty relative path or a relative descendant as contained, while rejecting
absolute relatives, the parent marker, and parent paths beginning with the
parent marker; preserve the existing root iteration and Windows case-insensitive
behavior.
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src/cognition/emergent/SandboxedToolForge.tssrc/cognition/emergent/__tests__/sandboxed-forge.test.ts
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Folded the review round ( Taken — four engines converged on it, and it is real. sourcery, qodo, Codex and CodeRabbit all landed on the same line: Worth noting the prefix form predates this PR; the realpath pass is what turned it into a visible denial, so it is fixed here rather than left behind. Half-taken — qodo's cached-roots finding. A root set containing an unresolvable entry is no longer cached, so a root that becomes readable later is not stranded. Deliberately not taken — per-read root re-resolution. A fully resolved root set stays pinned for the life of the forge. Re-resolving on every read would let anyone able to rewrite the root symlink relocate a running sandbox, which is precisely the move this check exists to stop; a caller that wants to follow a retargeted root constructs a new forge. That behavior is now pinned by a test (read A, repoint the link, second read refused, fresh forge sees B) and stated in the method docblock. The "initially absent root created later" half of that finding is not reachable in practice: the target's own Test count is now seven cases over a real temp-dir fixture. |
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@coderabbitai review @codex review (The containment predicate changed after your last pass — |
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Tip For best results, initiate chat on the files or code changes. 🧩 Analysis chain🏁 Script executed: #!/bin/bash
set -euo pipefail
ast-grep outline src/cognition/emergent/SandboxedToolForge.ts --items all
ast-grep outline src/cognition/emergent/__tests__/sandboxed-forge.test.ts --items all
printf '\n--- PR diff ---\n'
git diff --no-ext-diff --unified=80 HEAD^ HEAD -- \
src/cognition/emergent/SandboxedToolForge.ts \
src/cognition/emergent/__tests__/sandboxed-forge.test.ts
printf '\n--- Current SandboxedToolForge source ---\n'
cat -n src/cognition/emergent/SandboxedToolForge.ts
printf '\n--- Relevant test declarations ---\n'
rg -n -C 5 '(SandboxedToolForge|fsReadRoots|readFile|realpath|symlink|mkdtemp|afterAll|afterEach)' \
src/cognition/emergent/__tests__/sandboxed-forge.test.tsLength of output: 66226
I found no new issues in the updated containment predicate or root-resolution caching.
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Good catch, and it was mine to make — taken in full ( The root cache was all-or-nothing: Each root now caches on its own: a success is pinned for the life of the forge, a failure is dropped and retried, and neither touches a sibling. Regression test covers your exact shape — a symlink root plus a root that never exists, read, repoint, second read refused. @coderabbitai review — the containment predicate and the root cache have both changed since your last pass. |
🧩 Analysis chain🏁 Script executed: #!/bin/bash
set -euo pipefail
ast-grep outline src/cognition/emergent/SandboxedToolForge.ts --items all
ast-grep outline src/cognition/emergent/__tests__/sandboxed-forge.test.ts --items all
printf '\n--- commit 697238b diff ---\n'
git show --no-ext-diff --format=fuller --find-renames --find-copies --unified=100 697238b -- \
src/cognition/emergent/SandboxedToolForge.ts \
src/cognition/emergent/__tests__/sandboxed-forge.test.ts
printf '\n--- current forge source ---\n'
cat -n src/cognition/emergent/SandboxedToolForge.ts
printf '\n--- relevant test source ---\n'
cat -n src/cognition/emergent/__tests__/sandboxed-forge.test.ts
printf '\n--- cache and containment references ---\n'
rg -n -C 5 --type ts '(resolveReadRoots|readRootsCache|realpath|relative|fsReadRoots|readFile\s*\()' \
src/cognition/emergent/SandboxedToolForge.ts \
src/cognition/emergent/__tests__/sandboxed-forge.test.tsLength of output: 106991
The per-root cache now preserves the first successful resolution for each configured root. A failed resolution removes only that root from The mixed-root regression test covers the prior bypass. It verifies that retargeting The 🐇 ✅ ✏️ Learnings added
|
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@codex review — please re-read |
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Codex Review: Didn't find any major issues. 👍 Reviewed commit: ℹ️ About Codex in GitHubYour team has set up Codex to review pull requests in this repo. Reviews are triggered when you
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The sandboxed fs.readFile resolved the requested path with realpath before the containment check (#13). A path outside the read roots still reached the filesystem, so its ENOENT or EACCES showed whether a host path exists and is readable, and the blocked message printed where a host symlink points. The roots were compared unresolved, so a root that is itself a link (macOS /tmp links to /private/tmp) denied every read beneath it. The lexical check now runs first. A path that passes is resolved and checked again against the roots' own real paths, and the resolved path is what gets read.
…ng prefix A root that already ends in a separator (the filesystem root, a Windows drive root) was compared against a doubled separator, so every file beneath it was denied. path.relative has no such edge and applies the platform's own case rules. A root set containing an unresolvable entry is no longer cached, so a root that becomes readable later is not stranded; a fully resolved set stays pinned on purpose.
The root cache was all-or-nothing: One unresolvable root dropped the whole set, so the next read re-resolved the roots that had succeeded. A root symlink repointed in between was then followed to its new target, losing the pinning the cache exists to provide. Roots are now cached one by one: A success is pinned for the life of the forge, a failure is retried, and neither affects a sibling.
697238b to
5cdf53c
Compare
## <small>0.10.26 (2026-10-01)</small> * Merge branch 'master' into fix/cwe22-sandboxedtoolforge-sandboxed-772c ([54d1cce](54d1cce)) * Merge pull request #49 from framerslab/fix/sandbox-realpath-containment ([8e73959](8e73959)) * fix: resolve symlinks before path containment check in sandboxed fs.readFile ([bb087d8](bb087d8)) * fix(sandbox): check read paths lexically before resolving symlinks ([eb65e30](eb65e30)) * fix(sandbox): contain read paths with path.relative instead of a string prefix ([14f5642](14f5642)) * fix(sandbox): pin each resolved read root on its own ([5cdf53c](5cdf53c))
1 participant
Includes #13 by @andesyteoss, who found this symlink escape and fixed the read with
realpath. Their commit is in this branch unchanged, merged with current master so it diffs as text.This PR also checks the path against the roots before resolving it, resolves the configured roots, compares paths with
path.relative, pins each resolved root, and adds tests.The defect (CWE-22, live in master through 0.10.25)
SandboxedToolForge's sandboxedfs.readFilechecked containment withpath.resolve+startsWithand nothing else. A symlink that lives inside an allowed root resolves to an in-root string, passes the prefix check, and is then read through to its target anywhere on disk. The default root isprocess.cwd(), and a pnpmnode_modulesis a symlink farm, so no attacker-created link is required.Reachability: neither wilds-ai nor wunderland constructs the forge, so no first-party consumer is exposed.
The fix
../../etc/passwdbefore any filesystem call), thenrealpaththe target and re-check./tmp→/private/tmp); comparing a resolved file against an unresolved root would deny legitimate reads.Residual, documented in the code: a path component could be swapped for a link between
realpathandreadFile. Closing that needs anO_NOFOLLOWhandle, whichfs/promisesdoes not expose, and it requires local write access inside an allowed root.Tests
Eight cases in
sandboxed-forge.test.ts, on a real temp-dir fixture: an ordinary in-root read still works; a link inside the root pointing outside is blocked and its content never reaches the output; a plainly out-of-root path is still blocked by the lexical pass; the filesystem root works as a root; a sibling directory that shares a root's prefix is blocked; a root symlink repointed after the first read stays pinned; an unresolvable sibling root does not affect the others; and a root that is itself a symlink still resolves.Merging this publishes a patch release.
Summary by Sourcery
Harden sandboxed filesystem reads against symlink-based path traversal while retaining support for symlinked and filesystem roots.
Bug Fixes:
Enhancements:
Tests:
Summary by CodeRabbit