CWE - CWE-61: UNIX Symbolic Link (Symlink) Following (4.18)

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CWE Glossary Definition

CWE-61: UNIX Symbolic Link (Symlink) Following

Weakness ID: 61 (Structure: Composite) Composite - a Compound Element that consists of two or more distinct weaknesses, in which all weaknesses must be present at the same time in order for a potential vulnerability to arise. Removing any of the weaknesses eliminates or sharply reduces the risk. One weakness, X, can be "broken down" into component weaknesses Y and Z. There can be cases in which one weakness might not be essential to a composite, but changes the nature of the composite when it becomes a vulnerability.

Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities

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Description

The product, 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 product to operate on unauthorized files.

Extended Description

A product 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

symlink vulnerability

Common Consequences

Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Impact	Details
Read Files or Directories; Modify Files or Directories	Scope: Confidentiality, Integrity

Potential Mitigations

Phase(s)	Mitigation
Implementation	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.
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.

Composite Components

Nature	Type	ID	Name
Requires	ClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	340	Generation of Predictable Numbers or Identifiers
Requires	ClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	362	Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
Requires	BaseBase - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	386	Symbolic Name not Mapping to Correct Object
Requires	ClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	732	Incorrect Permission Assignment for Critical Resource

Relationships

Section Help This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

Relevant to the view "Research Concepts" (View-1000)

Nature	Type	ID	Name
ChildOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	59	Improper Link Resolution Before File Access ('Link Following')

Modes Of Introduction

Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Phase	Note
Implementation	These are typically reported for temporary files or privileged programs.

Applicable Platforms

Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

Class: Not Language-Specific (Undetermined Prevalence)

Likelihood Of Exploit

High

Selected Observed Examples

Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

Reference	Description
CVE-1999-1386	Some versions of Perl follow 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-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.
CVE-2015-3629	A Libcontainer used in Docker Engine allows local users to escape containerization and write to an arbitrary file on the host system via a symlink attack in an image when respawning a container.
CVE-2020-26277	In a MySQL database deployment tool, users may craft a maliciously packaged tarball that contains symlinks to files external to the target and once unpacked, will execute.
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.

Weakness Ordinalities

Ordinality	Description
Resultant	(where the weakness is typically related to the presence of some other weaknesses)

Functional Areas

File Processing

Affected Resources

File or Directory

Memberships

Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.

Nature	Type	ID	Name
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1404	Comprehensive Categorization: File Handling

Vulnerability Mapping Notes

Usage ALLOWED

(this CWE ID may be used to map to real-world vulnerabilities)

Reason Other

Rationale

This is a well-known Composite of multiple weaknesses that must all occur simultaneously, although it is attack-oriented in nature.

Comments

While attack-oriented composites are supported in CWE, they have not been a focus of research. There is a chance that future research or CWE scope clarifications will change or deprecate them. Perform root-cause analysis to determine which weaknesses allow symlink following to occur, and map to those weaknesses. For example, predictable file names might be intended functionality, but creation in a directory with insecure permissions might not.

Notes

Research Gap

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 [REF-493].

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
PLOVER	UNIX symbolic link following

Related Attack Patterns

CAPEC-ID	Attack Pattern Name
CAPEC-27	Leveraging Race Conditions via Symbolic Links

References

[REF-493] Steve Christey. "Second-Order Symlink Vulnerabilities". Bugtraq. 2005年06月07日.
<https://seclists.org/bugtraq/2005/Jun/44>. (URL validated: 2023年04月07日)

[REF-494] Shaun Colley. "Crafting Symlinks for Fun and Profit". Infosec Writers Text Library. 2004年04月12日.
<https://web.archive.org/web/20040502153535/http://www.infosecwriters.com/texts.php?op=display&id=159>. (URL validated: 2025年07月29日)

[REF-62] 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
Submission Date	Submitter	Organization
2006年07月19日 (CWE Draft 3, 2006年07月19日)	PLOVER
2006年07月19日 (CWE Draft 3, 2006年07月19日)
Modifications
Modification Date	Modifier	Organization
2025年09月09日 (CWE 4.18, 2025年09月09日)	CWE Content Team	MITRE
2025年09月09日 (CWE 4.18, 2025年09月09日)	updated Affected_Resources, Functional_Areas, References
2023年06月29日	CWE Content Team	MITRE
2023年06月29日	updated Mapping_Notes
2023年04月27日	CWE Content Team	MITRE
2023年04月27日	updated References, Relationships
2023年01月31日	CWE Content Team	MITRE
2023年01月31日	updated Description
2022年10月13日	CWE Content Team	MITRE
2022年10月13日	updated Observed_Examples
2022年04月28日	CWE Content Team	MITRE
2022年04月28日	updated Research_Gaps
2020年02月24日	CWE Content Team	MITRE
2020年02月24日	updated Relationships
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated Applicable_Platforms, Causal_Nature, Likelihood_of_Exploit, References, Relationships
2014年06月23日	CWE Content Team	MITRE
2014年06月23日	updated Modes_of_Introduction, Other_Notes
2012年10月30日	CWE Content Team	MITRE
2012年10月30日	updated Potential_Mitigations
2012年05月11日	CWE Content Team	MITRE
2012年05月11日	updated Observed_Examples, References
2011年06月01日	CWE Content Team	MITRE
2011年06月01日	updated Common_Consequences
2009年07月27日	CWE Content Team	MITRE
2009年07月27日	updated Observed_Examples
2008年10月14日	CWE Content Team	MITRE
2008年10月14日	updated Description
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Relationships, Observed_Example, Other_Notes, Research_Gaps, Taxonomy_Mappings, Weakness_Ordinalities
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Time_of_Introduction

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Page Last Updated: September 09, 2025

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