UNIX Hard Link

Opis

The product, when opening a file or directory, does not sufficiently account for when the name is associated with a hard link to a target that is outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files.

Failure for a system to check for hard links can result in vulnerability to different types of attacks. For example, an attacker can escalate their privileges if a file used by a privileged program is replaced with a hard link to a sensitive file (e.g. /etc/passwd). When the process opens the file, the attacker can assume the privileges of that process.

Skutki

• Confidentiality, Integrity

  Read Files or Directories; Modify Files or Directories

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-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-2005-0342 The Finder in Mac OS X and earlier allows local users to overwrite arbitrary files and gain privileges by creating a hard link from the .DS_Store file to an arbitrary file.
• CVE-2005-1111 Hard link race condition
• 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-2003-1366 setuid root tool allows attackers to read secret data by replacing a temp file with a hard link to a sensitive file

Słabość nadrzędna

• CWE-59 Improper Link Resolution Before File Access ('Link Following')

Kiedy powstaje

• Implementation

Dotyczy

Not Language-Specific, Unix, Not Technology-Specific

Źródła

1. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 9, "Hard Links", Page 518, Addison Wesley, 2006