CWE-367 Detail

CWE-367

Time-of-check Time-of-use (TOCTOU) Race Condition
MEDIUM
Incomplete
2006-07-19 00:00 +00:00
2023-06-29 00:00 +00:00

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Time-of-check Time-of-use (TOCTOU) Race Condition

The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state.

Extended Description

This weakness can be security-relevant when an attacker can influence the state of the resource between check and use. This can happen with shared resources such as files, memory, or even variables in multithreaded programs.

Informations

Modes Of Introduction

Implementation

Applicable Platforms

Language

Class: Not Language-Specific (Undetermined)

Common Consequences

Scope Impact Likelihood
Integrity
Other
Alter Execution Logic, Unexpected State

Note: The attacker can gain access to otherwise unauthorized resources.
Integrity
Other
Modify Application Data, Modify Files or Directories, Modify Memory, Other

Note: Race conditions such as this kind may be employed to gain read or write access to resources which are not normally readable or writable by the user in question.
Integrity
Other
Other

Note: The resource in question, or other resources (through the corrupted one), may be changed in undesirable ways by a malicious user.
Non-RepudiationHide Activities

Note: If a file or other resource is written in this method, as opposed to in a valid way, logging of the activity may not occur.
Non-Repudiation
Other
Other

Note: In some cases it may be possible to delete files a malicious user might not otherwise have access to, such as log files.

Observed Examples

Reference Description
CVE-2015-1743TOCTOU in sandbox process allows installation of untrusted browser add-ons by replacing a file after it has been verified, but before it is executed
CVE-2003-0813A multi-threaded race condition allows remote attackers to cause a denial of service (crash or reboot) by causing two threads to process the same RPC request, which causes one thread to use memory after it has been freed.
CVE-2004-0594PHP flaw allows remote attackers to execute arbitrary code by aborting execution before the initialization of key data structures is complete.
CVE-2008-2958chain: time-of-check time-of-use (TOCTOU) race condition in program allows bypass of protection mechanism that was designed to prevent symlink attacks.
CVE-2008-1570chain: time-of-check time-of-use (TOCTOU) race condition in program allows bypass of protection mechanism that was designed to prevent symlink attacks.

Potential Mitigations

Phases : Implementation
The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
Phases : Implementation
When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
Phases : Architecture and Design
Limit the interleaving of operations on files from multiple processes.
Phases : Implementation // Architecture and Design
If you cannot perform operations atomically and you must share access to the resource between multiple processes or threads, then try to limit the amount of time (CPU cycles) between the check and use of the resource. This will not fix the problem, but it could make it more difficult for an attack to succeed.
Phases : Implementation
Recheck the resource after the use call to verify that the action was taken appropriately.
Phases : Architecture and Design
Ensure that some environmental locking mechanism can be used to protect resources effectively.
Phases : Implementation
Ensure that locking occurs before the check, as opposed to afterwards, such that the resource, as checked, is the same as it is when in use.

Detection Methods

Automated Static Analysis

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
Effectiveness : High

Vulnerability Mapping Notes

Rationale : This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comments : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Related Attack Patterns

CAPEC-ID Attack Pattern Name
CAPEC-27 Leveraging Race Conditions via Symbolic Links
This attack leverages the use of symbolic links (Symlinks) in order to write to sensitive files. An attacker can create a Symlink link to a target file not otherwise accessible to them. When the privileged program tries to create a temporary file with the same name as the Symlink link, it will actually write to the target file pointed to by the attackers' Symlink link. If the attacker can insert malicious content in the temporary file they will be writing to the sensitive file by using the Symlink. The race occurs because the system checks if the temporary file exists, then creates the file. The attacker would typically create the Symlink during the interval between the check and the creation of the temporary file.
CAPEC-29 Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions
This attack targets a race condition occurring between the time of check (state) for a resource and the time of use of a resource. A typical example is file access. The adversary can leverage a file access race condition by "running the race", meaning that they would modify the resource between the first time the target program accesses the file and the time the target program uses the file. During that period of time, the adversary could replace or modify the file, causing the application to behave unexpectedly.

Notes

TOCTOU issues do not always involve symlinks, and not every symlink issue is a TOCTOU problem.
Non-symlink TOCTOU issues are not reported frequently, but they are likely to occur in code that attempts to be secure.

References

REF-18

The CLASP Application Security Process
Secure Software, Inc..
https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf

REF-367

Portably Solving File TOCTTOU Races with Hardness Amplification
Dan Tsafrir, Tomer Hertz, David Wagner, Dilma Da Silva.
https://www.usenix.org/legacy/events/fast08/tech/tsafrir.html

REF-44

24 Deadly Sins of Software Security
Michael Howard, David LeBlanc, John Viega.

REF-62

The Art of Software Security Assessment
Mark Dowd, John McDonald, Justin Schuh.

Submission

Name Organization Date Date Release Version
PLOVER 2006-07-19 +00:00 2006-07-19 +00:00 Draft 3

Modifications

Name Organization Date Comment
Eric Dalci Cigital 2008-07-01 +00:00 updated Time_of_Introduction
KDM Analytics 2008-08-01 +00:00 added/updated white box definitions
CWE Content Team MITRE 2008-09-08 +00:00 updated Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
CWE Content Team MITRE 2008-10-14 +00:00 updated Description, Name, Relationships
CWE Content Team MITRE 2008-11-24 +00:00 updated Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2009-01-12 +00:00 updated Alternate_Terms, Observed_Examples, Other_Notes, References, Relationship_Notes, Relationships, Research_Gaps
CWE Content Team MITRE 2009-05-27 +00:00 updated Demonstrative_Examples
KDM Analytics 2009-07-17 +00:00 Improved the White_Box_Definition
CWE Content Team MITRE 2009-07-27 +00:00 updated White_Box_Definitions
CWE Content Team MITRE 2010-09-27 +00:00 updated Description, Relationships
CWE Content Team MITRE 2010-12-13 +00:00 updated Alternate_Terms, Relationships
CWE Content Team MITRE 2011-06-01 +00:00 updated Common_Consequences
CWE Content Team MITRE 2011-06-27 +00:00 updated Common_Consequences
CWE Content Team MITRE 2011-09-13 +00:00 updated Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2012-05-11 +00:00 updated Demonstrative_Examples, Observed_Examples, References, Relationships
CWE Content Team MITRE 2012-10-30 +00:00 updated Potential_Mitigations
CWE Content Team MITRE 2014-07-30 +00:00 updated Demonstrative_Examples, Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2017-11-08 +00:00 updated Applicable_Platforms, Demonstrative_Examples, Likelihood_of_Exploit, References, Relationships, Taxonomy_Mappings, White_Box_Definitions
CWE Content Team MITRE 2019-06-20 +00:00 updated Relationships
CWE Content Team MITRE 2020-02-24 +00:00 updated References, Relationships
CWE Content Team MITRE 2022-04-28 +00:00 updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2022-06-28 +00:00 updated Observed_Examples
CWE Content Team MITRE 2023-01-31 +00:00 updated Description
CWE Content Team MITRE 2023-04-27 +00:00 updated Detection_Factors, References, Relationships
CWE Content Team MITRE 2023-06-29 +00:00 updated Mapping_Notes