Improper Link Resolution Before File Access ('Link Following')

Opis

The product 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.

Inne nazwy

insecure temporary file

Some people use the phrase "insecure temporary file" when referring to a link following weakness, but other weaknesses can produce insecure temporary files without any symlink involvement at all.

Zip Slip

"Zip slip" is an attack that uses file archives (e.g., ZIP, tar, rar, etc.) that contain filenames with path traversal sequences that cause the files to be written outside of the directory under which the archive is expected to be extracted [REF-1282]. It is most commonly used for relative path traversal (CWE-23) and link following (CWE-59).

Skutki

• Confidentiality, Integrity, Access Control

  Read Files or Directories; Modify Files or Directories; Bypass Protection 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 then an attacker may be able to bypass the mechanism.

• Other

  Execute Unauthorized Code or Commands

  Windows simple shortcuts, sometimes referred to as soft links, can be exploited remotely since a ".LNK" file can be uploaded like a normal file. This can enable remote execution.

Zapobieganie

• 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.

Przykłady podatności

• CVE-1999-1386 Some versions of Perl follow 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.
• CVE-2015-3629 A Libcontainer used in Docker Engine allows local users to escape containerization and write to an arbitrary file on the host system via a symlink attack in an image when respawning a container.
• CVE-2021-21272 "Zip Slip" vulnerability in Go-based Open Container Initiative (OCI) registries product allows writing arbitrary files outside intended directory via symbolic links or hard links in a gzipped tarball.
• CVE-2020-27833 "Zip Slip" vulnerability in container management product allows writing arbitrary files outside intended directory via a container image (.tar format) with filenames that are symbolic links that point to other files within the same tar file; however, the files being pointed to can also be symbolic links to destinations outside the intended directory, bypassing the initial check.

Słabość nadrzędna

• CWE-706 Use of Incorrectly-Resolved Name or Reference

Słabości podrzędne

• CWE-61 UNIX Symbolic Link (Symlink) Following
• CWE-62 UNIX Hard Link
• CWE-64 Windows Shortcut Following (.LNK)
• CWE-65 Windows Hard Link
• CWE-1386 Insecure Operation on Windows Junction / Mount Point

Kiedy powstaje

• Implementation — REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Dotyczy

Not Language-Specific, Windows, Unix, Not Technology-Specific

Uwagi

Link 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 predictability.

Źródła

1. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 9, "Symbolic Link Attacks", Page 518, Addison Wesley, 2006
2. Zip Slip Vulnerability — Snyk, 2018
3. State-of-the-Art Resources (SOAR) for Software Vulnerability Detection, Test, and Evaluation — Gregory Larsen, E. Kenneth Hong Fong, David A. Wheeler, Rama S. Moorthy, 2014