Tag Archives: UNIX Symbolic Link (Symlink) Following

CWE

CWE-61 – UNIX Symbolic Link (Symlink) Following

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Description

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

A software system that allows UNIX symbolic links (symlink) as part of paths whether in internal code or through user input can allow an attacker to spoof the symbolic link and traverse the file system to unintended locations or access arbitrary files. The symbolic link can permit an attacker to read/write/corrupt a file that they originally did not have permissions to access.

Modes of Introduction:

– Implementation

 

Likelihood of Exploit: High

 

Related Weaknesses

CWE-59
CWE-362
CWE-340
CWE-386
CWE-732

 

Consequences

Confidentiality, Integrity: Read Files or Directories, Modify Files or Directories

 

Potential Mitigations

Phase: Implementation

Description: 

Symbolic link attacks often occur when a program creates a tmp directory that stores files/links. Access to the directory should be restricted to the program as to prevent attackers from manipulating the files.

Phase: Architecture and Design

Description: 

CVE References

  • 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-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.