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Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

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ID

CWE-62: UNIX Hard Link

Weakness ID: 62
Abstraction: Variant
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The software, 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 software to operate on unauthorized files.

Extended Description

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.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

All

Operating Systems

UNIX

+ Common Consequences
ScopeEffect
Confidentiality
Integrity

Technical Impact: Read files or directories; Modify files or directories

+ Observed Examples
ReferenceDescription
Hard link attack, file overwrite; interesting because program checks against soft links
Hard link and possibly symbolic link following vulnerabilities in embedded operating system allow local users to overwrite arbitrary files.
Server creates hard links and unlinks files as root, which allows local users to gain privileges by deleting and overwriting arbitrary files.
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.
Web hosting manager follows hard links, which allows local users to read or modify arbitrary files.
Package listing system allows local users to overwrite arbitrary files via a hard link attack on the lockfiles.
Hard link race condition
OpenBSD chpass/chfn/chsh file content leak
+ Potential Mitigations

Phase: Architecture and Design

Strategy: 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.

+ Weakness Ordinalities
OrdinalityDescription
Resultant
(where the weakness is typically related to the presence of some other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base59Improper Link Resolution Before File Access ('Link Following')
Research Concepts (primary)1000
ChildOfCategoryCategory60UNIX Path Link Problems
Resource-specific Weaknesses (primary)631
Development Concepts (primary)699
ChildOfCategoryCategory743CERT C Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
ChildOfCategoryCategory877CERT C++ Secure Coding Section 09 - Input Output (FIO)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory980SFP Secondary Cluster: Link in Resource Name Resolution
Software Fault Pattern (SFP) Clusters (primary)888
PeerOfWeakness VariantWeakness Variant71Apple '.DS_Store'
Research Concepts1000
+ Research Gaps

Under-studied. It is likely that programs that check for symbolic links could be vulnerable to hard links.

+ Causal Nature

Explicit

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERUNIX hard link
CERT C Secure CodingFIO05-CIdentify files using multiple file attributes
CERT C++ Secure CodingFIO05-CPPIdentify files using multiple file attributes
Software Fault PatternsSFP18Link in resource name resolution
+ References
[REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 9, "Hard Links", Page 518.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Applicable_Platforms, Relationships, Taxonomy_Mappings, Weakness_Ordinalities
2008-10-14CWE Content TeamMITREInternal
updated Description
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2011-09-13CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Observed_Examples, References, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2014-07-30CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings

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Page Last Updated: January 18, 2017