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Race Conditions

Updated Jan 30, 2024 ·

Overview​

Race Conditions is a software vulnerability where the outcome depends on the timing of the events not matching the developer's intended order.

  • Computer is unexpectedly racing itself in the processing of certain types of data.
  • Multiple threads write the same variable in the same memory location simultaneously.
  • Can also be used against databases and file systems.

Dereferencing​

Dereferencing involves accessing the value or data stored at a particular memory address referenced by a pointer. It is a fundamental operation in programming, particularly in languages like C and C++.

  • Allows retrieval or modification of data at a specific memory address.
  • Pointers are used to store memory addresses that are then dereferenced to access the data.
  • Null Dereferencing, leads to crashes or undefined behavior if a null pointer is dereferenced.
  • Improper dereferencing can lead to buffer overflows and other vulnerabilities.

Dirty COW Exploit​

The Dirty COW (Copy-On-Write) exploit is a privilege escalation vulnerability in the Linux kernel that allows attackers to gain write access to read-only memory mappings.

  • CVE-2016-5195: Identified as a critical security vulnerability in 2016.
  • Exploits race condition in kernel's memory management, allowing local privilege escalation.
  • Bypasses the kernel's protection by exploiting how it handles the copy-on-write feature.
  • Used to overwrite sensitive files, escalate privileges, and execute arbitrary code.

Mitigations:

  • Apply kernel patches and updates.
  • Use security modules like SELinux to limit potential damage.

TOC Vulnerability​

A Time-of-Check (TOC) vulnerability occurs when a security-critical condition is verified, but the resource is not used immediately. This delay between the check and the use can be exploited.

  • Condition is checked, but resource use is delayed.
  • Attacker can change the state of the resource after it has been checked.
  • Examples include checking file permissions, then delaying file access.
  • Can lead to unauthorized access or inconsistent state.

TOU Vulnerability​

A Time-of-Use (TOU) vulnerability occurs when a resource is used based on the result of a previous check, but the resource's state may have changed in the meantime.

  • Resource is used based on a previous check.
  • Attacker can modify the resource after the check but before the use.
  • Examples: File content is checked, then modified before being read.
  • Can result in race conditions, privilege escalation, or data corruption.

Similar to TOC Vulnerability, but there's some difference on the focus of the vulnerability:

  • TOU Vulnerability focuses on the time the resource is used.
  • TOC Vulnerability focuses on the time the check is conducted.

Mitigations for TOC/TOU Vulnerabilities:

  • Use atomic operations to eliminate the gap between check and use.
  • Implement proper locking mechanisms to prevent concurrent access and ensure consistency.
  • Ensure the resource is used immediately after being checked, without delay.
  • Re-validate the resource's state immediately before use to ensure it hasn't changed.

TOE Vulnerability​

A Time-of-Event (TOE) vulnerability occurs when the state of a resource or system is assumed to remain constant between an event and subsequent actions based on that event. This can be exploited if an attacker can alter the state after the event has been triggered but before the dependent actions are performed.

  • Actions based on an event are delayed, allowing potential state changes.
  • Manipulation of data during a time window when a system is making a decision or evaluation.
  • Can lead to unauthorized access, privilege escalation, or data inconsistency.
  • Examples:
    • Triggering an event based on certain conditions, then changing those conditions before the event's effects are fully realized.
    • Checking user credentials, then altering user permissions before access is granted.

Mutex

  • Mutually exclusive flag that acts as gatekeeper to a section of code.
  • Ensures that only one thread can be processed at a time.
  • Concurrent execution will not be allowed, prevents race conditions.

Deadlock

  • Lock remains in place because process it's waiting for is terminated or crashed.
  • Can happen despite the processing being complete.
  • When this happens, system lose access to the resource until lock is removed.
  • To prevent deadlocks, test any locks or mutexes used inside the code.

Mitigations for TOE Vulnerabilities:

  • Ensure actions based on an event occur immediately after event is triggered, without delay.
  • Re-check state of resource immediately before performing actions, ensuring no changes.
  • Use synchronization mechanisms to handle events and dependent actions atomically.
  • Monitoring and logging to detect and respond to state changes that occur after an event but before actions are completed.