Status: Incomplete Compound Element ID: 61 (Compound Element Variant: Composite)Summary 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. Extended Description 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.
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. Follow the principle of least privilege when assigning access rights to files. 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. Fault: filename predictability, insecure directory permissions, non-atomic operations, race condition. These are typically reported for temporary files or privileged programs. Resultant (where the weakness
is typically related to the presence of some other
weaknesses)
Symlink vulnerabilities are regularly found in C and shell programs, but all programming languages can have this problem. Even shell programs are probably under-reported. "Second-order symlink vulnerabilities" may exist in programs that invoke other programs that follow symlinks. They are rarely reported but are likely to be fairly common when process invocation is used. Reference: [Christey2005]
Steve Christey. "Second-Order Symlink Vulnerabilities". Bugtraq. 2005-06-07. <http:/ Shaun Colley. "Crafting Symlinks for Fun and Profit". Infosec Writers Text Library. 2004-04-12. <http:/ Submissions PLOVER. (Externally Mined) Modifications Eric Dalci. Cigital. 2008-07-01. (External) updated Time_of_Introduction CWE Content Team. MITRE. 2008-09-08. (Internal) updated Relationships, Observed_Example, Other_Notes,
Research_Gaps, Taxonomy_Mappings,
Weakness_Ordinalities CWE Content Team. MITRE. 2008-10-14. (Internal) updated Description |
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May 26, 2009
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