The software writes to a buffer using an index or pointer that
references a memory location prior to the beginning of the buffer.
Extended Description
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.
Alternate Terms
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).
Time of Introduction
Architecture and Design
Implementation
Applicable Platforms
Languages
C
C++
Common Consequences
Scope
Effect
Availability
Out of bounds memory access will very likely result in the corruption
of relevant memory, and perhaps instructions, possibly leading to a
crash.
Access Control
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.
Other
When the consequence is arbitrary code execution, this can often be
used to subvert any other security service.
Likelihood of Exploit
Medium
Demonstrative Examples
Example 1
The following is an example of code that may result in a buffer
underwrite, if find() returns a negative value to indicate that ch is not
found in srcBuf:
Buffer underflow from an all-whitespace string,
which causes a counter to be decremented before the buffer while looking for
a non-whitespace character.
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).
Research Gaps
Much attention has been paid to buffer overflows, but "underflows"
sometimes exist in products that are relatively free of overflows, so it is
likely that this variant has been under-studied.
Causal Nature
Explicit
Taxonomy Mappings
Mapped Taxonomy Name
Node ID
Fit
Mapped Node Name
PLOVER
UNDER - Boundary beginning violation ('buffer
underflow'?)
Description
