908
Scope Impact Likelihood
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
The resource in question, or other resources (through the
corrupted one), may be changed in undesirable ways by a
malicious user.
Non-Repudiation Hide Activities
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
In some cases it may be possible to delete files a malicious
user might not otherwise have access to, such as log files.
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
Potential Mitigations
Phase: 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.
Phase: 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.
Phase: Architecture and Design
Limit the interleaving of operations on files from multiple processes.
Phase: Implementation
Phase: 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.
Phase: Implementation
Recheck the resource after the use call to verify that the action was taken appropriately.
Phase: Architecture and Design
Ensure that some environmental locking mechanism can be used to protect resources
effectively.
CWE Version 4.14
CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition
CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition