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Qualifier Challenge - KPRCA_00026


Original Versions

Known Vulnerabilities

  • CWE-122 - Heap-based Buffer Overflow
  • CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition
  • CWE-476 - NULL Pointer Dereference
  • CWEs are listed as indicated by the challenge author.

Scores

  • ForAllSecure: 0.06
  • CodeJitsu: 0.0
  • Disekt: 0.0
  • TECHx: 0.0
  • CSDS: 0.0
  • FuzzBOMB: 0.0
  • TrailofBits: 0.0
  • The maximum score for each challenge in CQE is 4, following the CQE Scoring Document.

Passed consensus evaluation

  • Disekt - CB1
  • ForAllSecure - CB1
  • FuzzBOMB - CB1
  • TECHx - CB1

Proved a POV in reference challenge

Defense against reference POVs

  • Disekt: 100.0% - CB1
  • ForAllSecure: 100.0% - CB1

No submission

  • Eighth Place Team
  • Eleventh Place Team
  • Fifth Place Team - Finalist
  • First Place Team - Finalist
  • Fourth Place Team - Finalist
  • Ninth Place Team
  • Second Place Team - Finalist
  • Seventh Place Team - Finalist
  • Sixth Place Team - Finalist
  • Tenth Place Team
  • Third Place Team - Finalist
  • Thirteenth Place Team
  • Twelfth Place Team

All Submissions

DARPA performer group

Kaprica Security (KPRCA)

Description

3M is a program that allows users to manage their memos. It provides a very simple interface with minimal yet useful features: create, modify, view, and delete. It supports auto-correction of misspelled words, where the user can specify custom corrections. In order to make the program more efficient, the latest version of the software uses threads!

Feature List

  • Create a memo
  • Prompts to fill in the following fields: subject, date, priority, and body.
  • Before it is added to the system, the validation on the input is done.
    • Must be valid year (1970-2500), month (1-12), and date (1-31).
    • Subject must not be longer than 32 alphanumeric characters.
    • Priority must be 0 (Low), 1 (Normal), or 2 (High).
    • Body must not be longer than 4096 bytes.
  • Displays the memo ID when successfully created.
  • Update a memo
  • Prompts for the memo ID.
  • Prompts to fill in the same fields as "create a memo" menu.
    • However, the user can leave the field empty to keep and use the original data.
  • Validation happens:
    • Memo ID must be valid (i.e. should be in the system)
    • Field validation (same as the memo creation)
  • Displays the memo ID when successfully update
  • View a memo
  • Prompts for the memo ID.
  • Memo ID must be valid (i.e. should be in the system)
  • Displays in a nice format
  • Delete a memo
  • Prompts for the memo ID.
  • Memo ID must be valid (i.e. should be in the system)
  • Removes the memo with the memo ID.
  • Add a custom auto-correction word
  • Prompts for the misspelled word.
  • Prompts for the correct word.
  • Adds the correction (misspelled->correct mapping) to the system
    • Each word must not be longer than 32 characters
    • The maximum number of correction entries is 100 (20 is pre-populated)
  • Quit
  • Quits the program.

Vulnerability

The vulnerability is the use of the shared resource without a proper lock in multi-threaded environment. In order to perform the auto-correction of the words when creating a memo, the program runs a separate thread (ac_process) that is in charge of checking the queue of words to be examined (ac_queue) and updating the words if they are in the auto-correction dictionary.

Since the user can add a custom auto-correction word such that a shorter string to be replaced by a longer string, a heap-based buffer overflow can happen. The program attempts to guarantee that ac_buffer will be large enough to copy in the next word. However, if the realloc triggers a call to allocate then a thread switch may occur, and because the realloc happens before ac_idx is incremented and is not guarded, ac_idx may be modified by the other thread. Thus, once realloc returns, there is not actually enough memory allocated for the memcpy. The fix is to put the call to realloc in the guarded code section.

There is also a NULL pointer dereference bug where the buffer is not initialized when recv failed within a different thread. The buffer needs to be checked after achieving the lock for the resource.

The effect of the buffer overflow is attacker control of the heap structures for the subsequent block. This should give the attacker the ability to trigger remote code execution.

Generic class of vulnerability

Heap Buffer Overlfow

TOCTOU (Time Of Check, Time Of Use) Error

NULL Pointer Dereference

CWE classification

Heap-based Buffer Overflow (CWE-122)

TOCTOU Error (CWE-367)

NULL Pointer Dereference (CWE-476)

Challenges

The competitors need to realize that this is a multi-threaded program, and be able to analyze the use of a shared resource (without any locking) among the threads. In order to trigger the bug, the fact that auto-correction does not safely handle the correction that increases in string length must be exploited.


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