Time-of-check to time-of-use: Difference between revisions

Revision as of 20:39, 8 December 2021

Revision as of 20:39, 8 December 2021

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In [[software development]], '''time-of-check to time-of-use''' ('''TOCTOU''', '''TOCTTOU''' or '''TOC/TOU''') is a class of [[software bug]]s caused by a [[race condition]] involving the ''checking'' of the state of a part of a system (such as a security credential) and the ''use'' of the results of that check.

TOCTOU race conditions are common in [[Unix]] between operations on the [[File system#Metadata|file system]],<ref>{{Cite web

[[Exploit (computer security)|e]] race condition for temporary files because it used<code>mp(</code><ref name="mktemp">{{cite web

| url=https://www.usenix.org/conference/fast-05/tocttou-vulnerabilities-unix-style-file-systems-anatomical-study

| title=TOCTTOU Vulnerabilities in UNIX-Style File Systems: An Anatomical Study

| last1=Wei

| first1=Jinpeng

| last2=Pu

| first2=Calton

| date=December 2005

| publisher=[[USENIX]]

| access-date=2019-01-14}}</ref> but can occur in other contexts, including local [[Unix ___domain socket|sockets]] and improper use of [[database transaction]]s. In the early 1990s, the mail utility of BSD 4.3 UNIX had an [[Exploit (computer security)|exploitable]] race condition for temporary files because it used the <code>mktemp()</code><ref name="mktemp">{{cite web

| url=https://man7.org/linux/man-pages/man3/mktemp.3.html

| title=mktemp(3)

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| archiveurl=https://archive.today/20130116041403/http://cdblp.cn/paper/UNIX%E7%9A%84%E4%B8%80%E4%B8%AA%E6%BC%8F%E6%B4%9E/94334.html

| archivedate=2013-01-16}}</ref>

Early versioversions of [[OpenSSH|SSH]] had an exploitable race condition for [[Unix ___domain sockets]].<ref>{{cite web

| last=Acheson

| first=Steve

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| url-status=dead

| archiveurl=https://web.archive.org/web/20170213004928/http://www.employees.org/~satch/ssh/faq/TheWholeSSHFAQ.html

| archivedate=2017-02-13 }}</ref> They remain a problem in modern systems; as of 2019, a TOCTOU race condition iin [[Docker (software)|erDocker]] allows root access to the filesystem of the host platform.<ref>{{Cite web

| url=https://duo.com/decipher/docker-bug-allows-root-access-to-host-file-system

| title=Docker Bug Allows Root Access to Host File System