COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONLive MITRE record

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.

Abstraction

Standard

Typical severity

High

Likelihood of attack

High

Understand the attack

What is this attack pattern?

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.

Execution flow

How does the attack proceed, step by step?

1

Explore

Attack step

The adversary explores to gauge what level of access they have.
2

Experiment

Attack step

The adversary confirms access to a resource on the target host. The adversary confirms ability to modify the targeted resource.
3

Exploit

Attack step

The adversary decides to leverage the 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 can replace the resource and cause an escalation of privilege.

Requirements

What does the attack require?

Prerequisites

  • A resource is access/modified concurrently by multiple processes.
  • The adversary is able to modify resource.
  • A race condition exists while accessing a resource.

Skills required

  • Medium: This attack can get sophisticated since the attack has to occur within a short interval of time.

Resources required

Not stated in the MITRE record.

Impact

What does a successful attack lead to?

Modify Data

Affected scopes: Integrity

Gain Privileges

Affected scopes: Confidentiality, Access Control, Authorization

Alter Execution Logic

Affected scopes: Confidentiality, Integrity, Availability

Read Data

Affected scopes: Confidentiality

Resource Consumption

Affected scopes: Availability

Defence

How is it prevented and mitigated?

1
Use safe libraries to access resources such as files.
2
Be aware that improper use of access function calls such as chown(), tempfile(), chmod(), etc. can cause a race condition.
3
Use synchronization to control the flow of execution.
4
Use static analysis tools to find race conditions.
5
Pay attention to concurrency problems related to the access of resources.

Real world

MITRE example instances

Example instance 1Detail
The Net Direct client for Linux before 6.0.5 in Nortel Application Switch 2424, VPN 3050 and 3070, and SSL VPN Module 1000 extracts and executes files with insecure permissions, which allows local users to exploit a race condition to replace a world-writable file in /tmp/NetClient and cause another user to execute arbitrary code when attempting to execute this client, as demonstrated by replacing /tmp/NetClient/client. See also: CVE-2007-1057
Example instance 2Detail
The following code illustrates a file that is accessed multiple times by name in a publicly accessible directory. A race condition exists between the accesses where an adversary can replace the file referenced by the name. include <sys/types.h> include <fcntl.h> include <unistd.h> define FILE "/tmp/myfile" define UID 100 void test(char *str) { int fd; fd = creat(FILE, 0644); if(fd == -1) return; chown(FILE, UID, -1); /* BAD */ close(fd); } int main(int argc, char **argv) { char *userstr; if(argc > 1) { userstr = argv[1]; test(userstr); } return 0; } [ REF-107 ]
CAPEC-29: Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions — DayBreach Saldırı Sözlüğü · DayBreach