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CWE-61: UNIX Symbolic Link (Symlink) Following
| | UNIX Symbolic Link (Symlink) Following |
Definition in a New Window 
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| Compound Element ID: 61 (Compound Element Variant: Composite) | | Status: Incomplete |
 Description
Description 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.
Alternate Terms
| Symlink following |
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| symlink vulnerability |
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Time of Introduction Common Consequences | Scope | Effect |
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Confidentiality Integrity | Technical Impact: Read files or
directories; Modify files or
directories |
Likelihood of Exploit Observed Examples | Reference | Description |
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| 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.
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| CVE-2003-0517 | Symlink attack allows local users to overwrite
files. |
| CVE-2004-0689 | Possible interesting
example |
| 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. |
Potential Mitigations
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. |
Other Notes
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Fault: filename predictability, insecure directory permissions, non-atomic
operations, race condition.
These are typically reported for temporary files or privileged
programs.
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Weakness Ordinalities | Ordinality | Description |
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Resultant | (where
the weakness is typically related to the presence of some other
weaknesses) |
Relationships Research Gaps
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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]
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Causal Nature Taxonomy Mappings | Mapped Taxonomy Name | Node ID | Fit | Mapped Node Name |
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| PLOVER | | | UNIX symbolic link following |
References
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[REF-7] Mark Dowd, John McDonald
and Justin Schuh. "The Art of Software Security Assessment". Chapter 9, "Symbolic Link Attacks", Page
518.. 1st Edition. Addison Wesley. 2006. |
Content History | Submissions |
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| Submission Date | Submitter | Organization | Source |
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| PLOVER | | Externally Mined | | | Modifications |
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| Modification Date | Modifier | Organization | Source |
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| 2008-07-01 | Eric Dalci | Cigital | External | | updated Time_of_Introduction | | 2008-09-08 | CWE Content Team | MITRE | Internal | | updated Relationships, Observed_Example, Other_Notes,
Research_Gaps, Taxonomy_Mappings,
Weakness_Ordinalities | | 2008-10-14 | CWE Content Team | MITRE | Internal | | updated Description | | 2009-07-27 | CWE Content Team | MITRE | Internal | | updated Observed_Examples | | 2011-06-01 | CWE Content Team | MITRE | Internal | | updated Common_Consequences | | 2012-05-11 | CWE Content Team | MITRE | Internal | | updated Observed_Examples, References |
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