Improper Link Resolution Before File Access ('Link Following')
|ID: 59||Date: (C)2012-05-14 (M)2018-01-10|
|Type: weakness||Status: DRAFT|
|Abstraction Type: Base|
The software attempts to access a file based on the filename,
but it does not properly prevent that filename from identifying a link or
shortcut that resolves to an unintended resource.
Likelihood of Exploit: Low to Medium
Applicable PlatformsLanguage Class: AllOperating System Class: SometimesOperating System Class: WindowsOperating System Class: OftenOperating System Class: UNIX
Time Of Introduction
Related Attack Patterns
|ConfidentialityIntegrityAccess_Control ||Read files or
directoriesModify files or
mechanism ||An attacker may be able to traverse the file system to unintended
locations and read or overwrite the contents of unexpected files. If the
files are used for a security mechanism than an attacker may be able to
bypass the mechanism. |
|Architecture and Design ||Separation of Privilege ||Follow the principle of least privilege when assigning access rights
to entities in a software system.Denying access to a file can prevent an attacker from replacing that
file with a link to a sensitive file. Ensure good compartmentalization
in the system to provide protected areas that can be trusted. || || |
RelationshipsLink following vulnerabilities are Multi-factor Vulnerabilities (MFV).
They are the combination of multiple elements: file or directory
permissions, filename predictability, race conditions, and in some cases, a
design limitation in which there is no mechanism for performing atomic file
creation operations.Some potential factors are race conditions, permissions, and
|CWE-59 ChildOf CWE-893 ||Category ||CWE-888 || |
- CVE-1999-1386 : Some versions of Perl follows symbolic links when running with the -e option, which allows local users to overwrite arbitrary files via a symlink attack.
- CVE-2000-1178 : Text editor follows symbolic links when creating a rescue copy during an abnormal exit, which allows local users to overwrite the files of other users.
- CVE-2004-0217 : Antivirus update allows local users to create or append to arbitrary files via a symlink attack on a logfile.
- CVE-2003-0517 : Symlink attack allows local users to overwrite files.
- CVE-2004-0689 : Window manager does not properly handle when certain symbolic links point to "stale" locations, which could allow local users to create or truncate arbitrary files.
- CVE-2005-1879 : Second-order symlink vulnerabilities
- CVE-2005-1880 : Second-order symlink vulnerabilities
- CVE-2005-1916 : Symlink in Python program
- CVE-2000-0972 : Setuid product allows file reading by replacing a file being edited with a symlink to the targeted file, leaking the result in error messages when parsing fails.
- CVE-2005-0824 : Signal causes a dump that follows symlinks.
- CVE-2001-1494 : Hard link attack, file overwrite; interesting because program checks against soft links
- CVE-2002-0793 : Hard link and possibly symbolic link following vulnerabilities in embedded operating system allow local users to overwrite arbitrary files.
- CVE-2003-0578 : Server creates hard links and unlinks files as root, which allows local users to gain privileges by deleting and overwriting arbitrary files.
- CVE-1999-0783 : Operating system allows local users to conduct a denial of service by creating a hard link from a device special file to a file on an NFS file system.
- CVE-2004-1603 : Web hosting manager follows hard links, which allows local users to read or modify arbitrary files.
- CVE-2004-1901 : Package listing system allows local users to overwrite arbitrary files via a hard link attack on the lockfiles.
- CVE-2005-1111 : Hard link race condition
- CVE-2000-0342 : Mail client allows remote attackers to bypass the user warning for executable attachments such as .exe, .com, and .bat by using a .lnk file that refers to the attachment, aka "Stealth Attachment."
- CVE-2001-1042 : FTP server allows remote attackers to read arbitrary files and directories by uploading a .lnk (link) file that points to the target file.
- CVE-2001-1043 : FTP server allows remote attackers to read arbitrary files and directories by uploading a .lnk (link) file that points to the target file.
- CVE-2005-0587 : Browser allows remote malicious web sites to overwrite arbitrary files by tricking the user into downloading a .LNK (link) file twice, which overwrites the file that was referenced in the first .LNK file.
- CVE-2001-1386 : ".LNK." - .LNK with trailing dot
- CVE-2003-1233 : Rootkits can bypass file access restrictions to Windows kernel directories using NtCreateSymbolicLinkObject function to create symbolic link
- CVE-2002-0725 : File system allows local attackers to hide file usage activities via a hard link to the target file, which causes the link to be recorded in the audit trail instead of the target file.
- CVE-2003-0844 : Web server plugin allows local users to overwrite arbitrary files via a symlink attack on predictable temporary filenames.
For more examples, refer to CVE relations in the bottom box.
White Box Definitions None
Black Box Definitions None
|PLOVER || ||Link Following || |
|CERT C Secure Coding ||FIO02-C ||Canonicalize path names originating from untrusted
sources || |
|CERT C Secure Coding ||POS01-C ||Check for the existence of links when dealing with
files || |
|CERT C++ Secure Coding ||FIO02-CPP ||Canonicalize path names originating from untrusted
sources || |
- Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 9, "Symbolic Link Attacks", Page
518.'. Published on 2006.