high
8.6
CWE
22 59
Advisory Published
Advisory Published
Updated

CVE-2021-37712: Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning using symbolic links

First published: Tue Aug 31 2021(Updated: )

### Impact Arbitrary File Creation, Arbitrary File Overwrite, Arbitrary Code Execution node-tar aims to guarantee that any file whose location would be modified by a symbolic link is not extracted. This is, in part, achieved by ensuring that extracted directories are not symlinks. Additionally, in order to prevent unnecessary stat calls to determine whether a given path is a directory, paths are cached when directories are created. This logic was insufficient when extracting tar files that contained two directories and a symlink with names containing unicode values that normalized to the same value. Additionally, on Windows systems, long path portions would resolve to the same file system entities as their 8.3 "short path" counterparts. A specially crafted tar archive could thus include directories with two forms of the path that resolve to the same file system entity, followed by a symbolic link with a name in the first form, lastly followed by a file using the second form. It led to bypassing node-tar symlink checks on directories, essentially allowing an untrusted tar file to symlink into an arbitrary location and subsequently extracting arbitrary files into that location, thus allowing arbitrary file creation and overwrite. The v3 branch of `node-tar` has been deprecated and did not receive patches for these issues. If you are still using a v3 release we recommend you update to a more recent version of `node-tar`. If this is not possible, a workaround is available below. ### Patches 6.1.9 || 5.0.10 || 4.4.18 ### Workarounds Users may work around this vulnerability without upgrading by creating a custom filter method which prevents the extraction of symbolic links. ```js const tar = require('tar') tar.x({ file: 'archive.tgz', filter: (file, entry) => { if (entry.type === 'SymbolicLink') { return false } else { return true } } }) ``` Users are encouraged to upgrade to the latest patched versions, rather than attempt to sanitize tar input themselves. #### Fix The problem is addressed in the following ways, when comparing paths in the directory cache and path reservation systems: 1. The `String.normalize('NFKD')` method is used to first normalize all unicode to its maximally compatible and multi-code-point form. 2. All slashes are normalized to `/` on Windows systems (on posix systems, `\` is a valid filename character, and thus left intact). 3. When a symbolic link is encountered on Windows systems, the entire directory cache is cleared. Collisions related to use of 8.3 short names to replace directories with other (non-symlink) types of entries may make archives fail to extract properly, but will not result in arbitrary file writes.

Credit: security-advisories@github.com security-advisories@github.com

Affected SoftwareAffected VersionHow to fix
redhat/rh-nodejs14-nodejs<0:14.18.2-1.el7
0:14.18.2-1.el7
redhat/rh-nodejs14-nodejs-nodemon<0:2.0.3-6.el7
0:2.0.3-6.el7
redhat/rh-nodejs12-nodejs<0:12.22.12-2.el7
0:12.22.12-2.el7
Npmjs Tar<=4.4.17
Npmjs Tar>=5.0.0<=5.0.9
Npmjs Tar>=6.0.0<=6.1.8
Microsoft Windows
Debian Debian Linux=10.0
Debian Debian Linux=11.0
Oracle GraalVM=20.3.3
Oracle GraalVM=21.2.0
Siemens Sinec Infrastructure Network Services<1.0.1.1
debian/node-tar<=4.4.6+ds1-3+deb10u1
4.4.6+ds1-3+deb10u2
6.0.5+ds1+~cs11.3.9-1+deb11u2
6.1.13+~cs7.0.5-1
redhat/nodejs-tar<4.4.18
4.4.18
redhat/nodejs-tar<5.0.10
5.0.10
redhat/nodejs-tar<6.1.9
6.1.9
npm/tar>=3.0.0<4.4.18
4.4.18
npm/tar>=6.0.0<6.1.9
6.1.9
npm/tar>=5.0.0<5.0.10
5.0.10
All of
Any of
Npmjs Tar<=4.4.17
Npmjs Tar>=5.0.0<=5.0.9
Npmjs Tar>=6.0.0<=6.1.8
Microsoft Windows

Remedy

https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf

Remedy

https://github.com/npm/node-tar/security/advisories/GHSA-qq89-hq3f-393p

Remedy

https://www.oracle.com/security-alerts/cpuoct2021.html

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Reference Links

Parent vulnerabilities

(Appears in the following advisories)

Frequently Asked Questions

  • What is the vulnerability ID of this flaw in the npm package tar?

    The vulnerability ID is CVE-2021-37712.

  • What is the impact of CVE-2021-37712?

    The impact includes Arbitrary File Creation, Arbitrary File Overwrite, and Arbitrary Code Execution.

  • Which versions of the npm package tar are affected by CVE-2021-37712?

    Versions between 4.4.18 and 6.1.9 of the npm package tar are affected.

  • How can I fix the vulnerability CVE-2021-37712?

    To fix the vulnerability, update the npm package tar to version 6.1.9 or higher.

  • Where can I find more information about CVE-2021-37712?

    You can find more information about CVE-2021-37712 on the NVD website.

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