GNU Wget creates arbitrary symbolic links during recursive FTP download

Overview

GNU wget allows arbitrary filesystem access when creating symbolic links during a recursive FTP download. This allows an attacker to overwrite files with the permissions of the user running wget.

Description

CWE-59:** CWE-59: Improper Link Resolution Before File Access (‘Link Following’)**

Wget is a common Unix utility to retrieve remote files. When wget is running in recursive mode (the -m or -r switch) with a FTP server as the destination, it is vulnerable to a link following attack. A malicious FTP server, when configured to provide symlinks in the directory listing, can force the client wget utility to enter into the the specified local symlink, navigating the local file system for the attacker. Wget will then download and create or overwrite existing files within the local symlink, setting permissions to those of the remote files.

See the Rapid7 advisory for more details.

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Impact

A remote unauthenticated malicious FTP server, connected to the victim via wget, can create and overwrite arbitrary files in the context of the user running wget.

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Solution

Apply an Update

This vulnerability is addressed in wget 1.16. Updates should also be available in various package formats for downstream Linux distributions. Check your distribution’s package management system for updates.

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Enable wget symlink traversal

In wget versions 1.15 and earlier, configure retr-symlinks=on in /etc/wgetrc or ~/.wgetrc or specify --retr-symlinks as a command line option to wget.

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Vendor Information

685996

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GNU wget Affected

Updated: October 28, 2014

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

CVSS Metrics

Group	Score	Vector
Base	5.8	AV:N/AC:M/Au:N/C:N/I:P/A:P
Temporal	4.8	E:F/RL:OF/RC:C
Environmental	3.6	CDP:ND/TD:M/CR:ND/IR:ND/AR:ND

References

• <http://git.savannah.gnu.org/cgit/wget.git/commit/?id=18b0979357ed7dc4e11d4f2b1d7e0f5932d82aa7&gt;
• <http://cwe.mitre.org/data/definitions/59.html&gt;
• <https://bugzilla.redhat.com/show_bug.cgi?id=1139181&gt;
• <https://community.rapid7.com/community/metasploit/blog/2014/10/28/r7-2014-15-gnu-wget-ftp-symlink-arbitrary-filesystem-access&gt;
• <http://www.gnu.org/software/wget/manual/wget.html#index-symbolic-links_002c-retrieving&gt;
• <http://gnu.huihoo.org/wget-1.8.1/html_node/wget_10.html&gt;
• <http://comments.gmane.org/gmane.comp.web.wget.general/10367&gt;

Acknowledgements

Thanks to HD Moore and John Hart of Rapid7, Inc. for reporting this vulnerability.

This document was written by Chris King.

Other Information

CVE IDs:	CVE-2014-4877
Date Public:	2014-10-27 Date First Published: