Time of check, time of use race condition
#REDIRECT Race Conditions
Last revision (mm/dd/yy): 04/7/2009
Time-of-check, time-of-use race conditions occur when between the time in which a given resource is checked, and the time that resource is used, a change occurs in the resource to invalidate the results of the check.
- Access control: The attacker can gain access to otherwise unauthorized resources.
- Authorization: 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: The resource in question, or other resources (through the corrupted one), may be changed in undesirable ways by a malicious user.
- Accountability: 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: In some cases it may be possible to delete files a malicious user might not otherwise have access to, such as log files.
- Design: Strong locking methods may be designed to protect against this flaw.
- Implementation: Use of system APIs may prevent check, use race conditions.
- Languages: Any
- Platforms: All
- Some access to the resource in question
Likelihood of exploit
Low to Medium
Time-of-check, time-of-use race conditions occur when a resource is checked for a particular value, that value is changed, then the resource is used, based on the assumption that the value is still the same as it was at check time.
This is a broad category of race condition encompassing binding flaws, locking race conditions, and others.
struct stat *sb; .. lstat("...",sb); // it has not been updated since the last time it was read printf("stated file\n"); if (sb->st_mtimespec==...) print("Now updating things\n"); updateThings(); }
Potentially the file could have been updated between the time of the check and the lstat, especially since the printf has latency.
- Design: Ensure that some environmental locking mechanism can be used to protect resources effectively.
- 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.
Related Technical Impacts