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How the CVE Works
The vulnerability resides in the `OpenShellFsBridge.readFile` function of the OpenClaw npm package. The function followed a classic check-then-act pattern, which is susceptible to a Time-of-Check Time-of-Use (TOCTOU) race condition. The file system bridge would first validate that a requested path was within the sandbox’s mount root. Once validated, it would then read the file from the host file system using that same path string. An attacker with sandbox access could exploit the time window between the validation check and the actual file read. By rapidly swapping a parent directory with a symlink that points outside the sandbox, the attacker could cause the subsequent read operation to target a file outside the intended mount root, leading to unauthorized information disclosure. The issue was exacerbated on platforms that do not support the `O_NOFOLLOW` flag for opening files, as the fix relied on more complex ancestor walking logic.
dailycve form (3 words max per line):
Platform: OpenClaw (npm)
Version: <=2026.4.21
Vulnerability: TOCTOU race
Severity: Moderate
date: 2026-04-23
Prediction: 2026-04-23
What Undercode Say: Analytics
The following Bash commands can be used to check the installed version of OpenClaw and verify if a system is vulnerable.
Check current OpenClaw version npm list openclaw Directly inspect package.json for openclaw version cat node_modules/openclaw/package.json | grep version Git-based version detection (if installed from source) cd /path/to/openclaw && git describe --tags
A proof-of-concept script to test for the TOCTOU vulnerability by simulating a symlink swap:
!/bin/bash
PoC: Simulate symlink swap race condition
Note: Requires sandboxed environment for accurate testing
Setup sandbox and target file outside root
SANDBOX_ROOT="./sandbox_mount"
mkdir -p "$SANDBOX_ROOT/valid/path"
Target file outside sandbox (sensitive data)
HOST_TARGET="/etc/passwd"
Start the check-then-read loop
for i in {1..1000}
do
Background process to swap symlink after validation but before read
(
ln -sf "$SANDBOX_ROOT/valid/path" "$SANDBOX_ROOT/valid/tmp"
sleep 0.01
rm "$SANDBOX_ROOT/valid/tmp"
ln -sf "$HOST_TARGET" "$SANDBOX_ROOT/valid/tmp"
) &
Trigger the vulnerable read function
(Hypothetical command that calls OpenShellFsBridge.readFile)
openclaw read "$SANDBOX_ROOT/valid/tmp/sensitive"
wait
done
Exploit
The core of the exploit lies in winning the race between path validation and file read. An attacker would:
1. Prepare the Environment: Create a sandboxed environment with write access, such as a CI job or plugin that can create symlinks.
2. Create a Dangling Symlink: Inside the sandbox, create a directory symlink pointing to a valid, safe location (e.g., link -> valid/path).
3. Spawn Race Processes:
Thread A (Victim): Call `readFile` on a path inside the symlink (e.g., sandbox/link/secret.txt).
Thread B (Attacker): Continuously flip the symlink target between a safe, existing directory (e.g., valid/path) and the attacker’s desired target outside the sandbox (e.g., /etc/passwd).
4. Win the Race: If the attacker’s thread successfully swaps the symlink target after the validation check (which sees the safe path) but before the `read` system call, the read will be performed on the file outside the sandbox.
5. Data Exfiltration: The content of files outside the sandbox, such as environment variables, configuration files, or SSH keys, can be read and transmitted to an external server via a webhook or log message.
Protection from this CVE
The primary protection is to update to the fixed version. Additional defense-in-depth measures include:
Immediate Upgrade: Update the `openclaw` package to version 2026.4.22 or later.
npm install [email protected] Or globally npm install -g [email protected]
Verify Integrity: After updating, confirm the package has not been tampered with. The fix commit, 95119017, is included only in v2026.4.22 and later.
npm audit signatures | grep openclaw
Kernel Restrictions (Linux/BSD):
Restrict symlink following for the OpenClaw process using `fs.protected_regular` and `fs.protected_symlinks` sysctls.
Run OpenClaw in a restricted container or a dedicated user namespace with limited privileges.
Enable symlink protections system-wide (requires root) sysctl -w fs.protected_symlinks=1 sysctl -w fs.protected_regular=2
Filesystem Limitations (Windows):
Policy restrictions for creating symlinks (SeCreateSymbolicLinkPrivilege) for the OpenClaw service account.
Use a directory with DisableReparsePoints=1 as the sandbox mount point.
Impact
If left unpatched, this vulnerability could allow an attacker with moderate access to the system to break out of the OpenClaw sandbox environment. The potential impacts include:
Confidentiality Breach: Reading sensitive host system files (e.g., /etc/passwd, /etc/shadow, application secrets, and environment variables) that the OpenClaw process user has permissions to access.
Privilege Escalation:
By reading process memory or configuration files, an attacker could obtain session tokens or API keys to pivot to other internal services.
In environments where OpenClaw runs with elevated privileges (e.g., for hardware access), the attacker could potentially read cryptographic keys.
Information Leakage: Exposure of system metadata, directory listings, and file content that can be used for further reconnaissance or chaining with other exploits (e.g., CVE-2026-25593 for RCE).
Circumvention of Security Controls: The sandbox is designed to isolate untrusted workloads; this vulnerability completely bypasses that isolation for read operations, undermining the system’s entire trust model.
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Sources:
Reported By: github.com
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