Buffer Underwrite ('Buffer Underflow')

Opis

The product writes to a buffer using an index or pointer that references a memory location prior to the beginning of the buffer.

Inne nazwy

buffer underrun

Some prominent vendors and researchers use the term "buffer underrun". "Buffer underflow" is more commonly used, although both terms are also sometimes used to describe a buffer under-read (CWE-127).

Skutki

• Integrity, Availability

  Modify Memory; DoS: Crash, Exit, or Restart

  Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash.

• Integrity, Confidentiality, Availability, Access Control, Other

  Execute Unauthorized Code or Commands; Modify Memory; Bypass Protection Mechanism; Other

  If the corrupted memory can be effectively controlled, it may be possible to execute arbitrary code. If the corrupted memory is data rather than instructions, the system will continue to function with improper changes, possibly in violation of an implicit or explicit policy. The consequences would only be limited by how the affected data is used, such as an adjacent memory location that is used to specify whether the user has special privileges.

• Access Control, Other

  Bypass Protection Mechanism; Other

  When the consequence is arbitrary code execution, this can often be used to subvert any other security service.

Zapobieganie

• Requirements

  Choose a language that is not susceptible to these issues.

• Implementation

  All calculated values that are used as index or for pointer arithmetic should be validated to ensure that they are within an expected range.

Przykłady podatności

• CVE-2021-24018 buffer underwrite in firmware verification routine allows code execution via a crafted firmware image
• CVE-2002-2227 Unchecked length of SSLv2 challenge value leads to buffer underflow.
• CVE-2007-4580 Buffer underflow from a small size value with a large buffer (length parameter inconsistency, CWE-130)
• CVE-2007-1584 Buffer underflow from an all-whitespace string, which causes a counter to be decremented before the buffer while looking for a non-whitespace character.
• CVE-2007-0886 Buffer underflow resultant from encoded data that triggers an integer overflow.
• CVE-2006-6171 Product sets an incorrect buffer size limit, leading to "off-by-two" buffer underflow.
• CVE-2006-4024 Negative value is used in a memcpy() operation, leading to buffer underflow.
• CVE-2004-2620 Buffer underflow due to mishandled special characters

Słabość nadrzędna

• CWE-786 Access of Memory Location Before Start of Buffer
• CWE-787 Out-of-bounds Write

Kiedy powstaje

• Implementation — This typically occurs when a pointer or its index is decremented to a position before the buffer, when pointer arithmetic results in a position before the beginning of the valid memory location, or when a negative index is used.

Dotyczy

Memory-Unsafe, C, C++

Uwagi

This could be resultant from several errors, including a bad offset or an array index that decrements before the beginning of the buffer (see CWE-129).

Źródła

1. Buffer UNDERFLOWS: What do you know about it? — Vuln-Dev Mailing List, 2004
2. 24 Deadly Sins of Software Security — Michael Howard, David LeBlanc, John Viega, "Sin 5: Buffer Overruns." Page 89, McGraw-Hill, 2010
3. AddressSanitizer