CVE-2021-32804 (published 2021-08-03T19:15Z)

The npm package "tar" (aka node-tar) before versions 6.1.1, 5.0.6, 4.4.14, and 3.3.2 has a arbitrary File Creation/Overwrite vulnerability due to insufficient absolute path sanitization. node-tar aims to prevent extraction of absolute file paths by turning absolute paths into relative paths when the `preservePaths` flag is not set to `true`. This is achieved by stripping the absolute path root from any absolute file paths contained in a tar file. For example `/home/user/.bashrc` would turn into `home/user/.bashrc`. This logic was insufficient when file paths contained repeated path roots such as `////home/user/.bashrc`. `node-tar` would only strip a single path root from such paths. When given an absolute file path with repeating path roots, the resulting path (e.g. `///home/user/.bashrc`) would still resolve to an absolute path, thus allowing arbitrary file creation and overwrite. This issue was addressed in releases 3.2.2, 4.4.14, 5.0.6 and 6.1.1. Users may work around this vulnerability without upgrading by creating a custom `onentry` method which sanitizes the `entry.path` or a `filter` method which removes entries with absolute paths. See referenced GitHub Advisory for details. Be aware of CVE-2021-32803 which fixes a similar bug in later versions of tar.

Severity: MEDIUM
CVSS v2 base score: 5.8 (AV:N/AC:M/Au:N/C:N/I:P/A:P)
CVSS v3 base score: 8.1, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H)

Weakness information:
cwe_id: CWE-22
cwe_name: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
description: The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
extended_description: 
            Many file operations are intended to take place within a restricted directory. By using special elements such as ".." and "/" separators, attackers can escape outside of the restricted location to access files or directories that are elsewhere on the system. One of the most common special elements is the "../" sequence, which in most modern operating systems is interpreted as the parent directory of the current location. This is referred to as relative path traversal. Path traversal also covers the use of absolute pathnames such as "/usr/local/bin" to access unexpected files. This is referred to as absolute path traversal.
         
         

Fix information:
repo_url: https://github.com/npm/node-tar
commit_details: repo_url: https://github.com/npm/node-tar
author: isaacs
author_date: 2021-07-23 15:27:25-07:00
msg: fix: strip absolute paths more comprehensively
repository: repo_url: https://github.com/npm/node-tar
repo_name: isaacs/node-tar
description: tar for node
repo_language: JavaScript
owner: npm
file_changes: filename: strip-absolute-path.js
change_type: ModificationType.ADD
diff: @@ -0,0 +1,14 @@
+// unix absolute paths are also absolute on win32, so we use this for both
+const { isAbsolute, parse } = require('path').win32
+
+// returns [root, stripped]
+module.exports = path => {
+  let r = ''
+  while (isAbsolute(path)) {
+    // windows will think that //x/y/z has a "root" of //x/y/
+    const root = path.charAt(0) === '/' ? '/' : parse(path).root
+    path = path.substr(root.length)
+    r += root
+  }
+  return [r, path]
+}

programming_language: CoffeeScript
filename: unpack.js
change_type: ModificationType.MODIFY
diff: @@ -14,6 +14,7 @@ const path = require('path')
 const mkdir = require('./mkdir.js')
 const wc = require('./winchars.js')
 const pathReservations = require('./path-reservations.js')
+const stripAbsolutePath = require('./strip-absolute-path.js')
 
 const ONENTRY = Symbol('onEntry')
 const CHECKFS = Symbol('checkFs')
@@ -224,11 +225,10 @@ class Unpack extends Parser {
 
       // absolutes on posix are also absolutes on win32
       // so we only need to test this one to get both
-      if (path.win32.isAbsolute(p)) {
-        const parsed = path.win32.parse(p)
-        entry.path = p.substr(parsed.root.length)
-        const r = parsed.root
-        this.warn('TAR_ENTRY_INFO', `stripping ${r} from absolute path`, {
+      const [root, stripped] = stripAbsolutePath(p)
+      if (root) {
+        entry.path = stripped
+        this.warn('TAR_ENTRY_INFO', `stripping ${root} from absolute path`, {
           entry,
           path: p,
         })

programming_language: JavaScript
filename: write-entry.js
change_type: ModificationType.MODIFY
diff: @@ -23,6 +23,7 @@ const CLOSE = Symbol('close')
 const MODE = Symbol('mode')
 const warner = require('./warn-mixin.js')
 const winchars = require('./winchars.js')
+const stripAbsolutePath = require('./strip-absolute-path.js')
 
 const modeFix = require('./mode-fix.js')
 
@@ -52,12 +53,12 @@ const WriteEntry = warner(class WriteEntry extends MiniPass {
       this.on('warn', opt.onwarn)
 
     let pathWarn = false
-    if (!this.preservePaths && path.win32.isAbsolute(p)) {
-      // absolutes on posix are also absolutes on win32
-      // so we only need to test this one to get both
-      const parsed = path.win32.parse(p)
-      this.path = p.substr(parsed.root.length)
-      pathWarn = parsed.root
+    if (!this.preservePaths) {
+      const [root, stripped] = stripAbsolutePath(this.path)
+      if (root) {
+        this.path = stripped
+        pathWarn = root
+      }
     }
 
     this.win32 = !!opt.win32 || process.platform === 'win32'
@@ -351,10 +352,12 @@ const WriteEntryTar = warner(class WriteEntryTar extends MiniPass {
       this.on('warn', opt.onwarn)
 
     let pathWarn = false
-    if (path.isAbsolute(this.path) && !this.preservePaths) {
-      const parsed = path.parse(this.path)
-      pathWarn = parsed.root
-      this.path = this.path.substr(parsed.root.length)
+    if (!this.preservePaths) {
+      const [root, stripped] = stripAbsolutePath(this.path)
+      if (root) {
+        this.path = stripped
+        pathWarn = root
+      }
     }
 
     this.remain = readEntry.size

programming_language: JavaScript
filename: strip-absolute-path.js
change_type: ModificationType.ADD
diff: @@ -0,0 +1,14 @@
+const t = require('tap')
+const stripAbsolutePath = require('../lib/strip-absolute-path.js')
+
+const cases = {
+  '/': ['/', ''],
+  '////': ['////', ''],
+  'c:///a/b/c': ['c:///', 'a/b/c'],
+  '\\\\foo\\bar\\baz': ['\\\\foo\\bar\\', 'baz'],
+  '//foo//bar//baz': ['//', 'foo//bar//baz'],
+  'c:\\c:\\c:\\c:\\\\d:\\e/f/g': ['c:\\c:\\c:\\c:\\\\d:\\', 'e/f/g'],
+}
+
+for (const [input, [root, stripped]] of Object.entries(cases))
+  t.strictSame(stripAbsolutePath(input), [root, stripped], input)

programming_language: CoffeeScript
filename: unpack.js
change_type: ModificationType.MODIFY
diff: @@ -776,6 +776,9 @@ t.test('absolute paths', t => {
   })
 
   const absolute = path.resolve(dir, 'd/i/r/absolute')
+  const root = path.parse(absolute).root
+  const extraAbsolute = root + root + root + absolute
+  t.ok(path.isAbsolute(extraAbsolute))
   t.ok(path.isAbsolute(absolute))
   const parsed = path.parse(absolute)
   const relative = absolute.substr(parsed.root.length)
@@ -783,7 +786,7 @@ t.test('absolute paths', t => {
 
   const data = makeTar([
     {
-      path: absolute,
+      path: extraAbsolute,
       type: 'File',
       size: 1,
       atime: new Date('1979-07-01T19:10:00.000Z'),
@@ -798,7 +801,7 @@ t.test('absolute paths', t => {
   t.test('warn and correct', t => {
     const check = t => {
       t.match(warnings, [[
-        'stripping / from absolute path',
+        `stripping ${root}${root}${root}${root} from absolute path`,
         { path: absolute, code: 'TAR_ENTRY_INFO' },
       ]])
       t.ok(fs.lstatSync(path.resolve(dir, relative)).isFile(), 'is file')

programming_language: JavaScript
filename: write-entry.js
change_type: ModificationType.MODIFY
diff: @@ -385,7 +385,10 @@ t.test('nonexistent file', t => {
 })
 
 t.test('absolute path', t => {
-  const f = path.resolve(files, '512-bytes.txt')
+  const absolute = path.resolve(files, '512-bytes.txt')
+  const { root } = path.parse(absolute)
+  const f = root + root + root + absolute
+  const warn = root + root + root + root
   t.test('preservePaths=false strict=false', t => {
     const warnings = []
     const ws = new WriteEntry(f, {
@@ -398,13 +401,13 @@ t.test('absolute path', t => {
       out = Buffer.concat(out)
       t.equal(out.length, 1024)
       t.match(warnings, [[
-        'TAR_ENTRY_INFO', /stripping .* from absolute path/, { path: f },
+        'TAR_ENTRY_INFO', `stripping ${warn} from absolute path`, { path: f },
       ]])
 
       t.match(ws.header, {
         cksumValid: true,
         needPax: false,
-        path: f.replace(/^(\/|[a-z]:\\\\)/, ''),
+        path: f.replace(/^(\/|[a-z]:\\\\){4}/, ''),
         mode: 0o644,
         size: 512,
         linkpath: null,

programming_language: JavaScript