Numeric Truncation Error

Opis

Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.

When a primitive is cast to a smaller primitive, the high order bits of the large value are lost in the conversion, potentially resulting in an unexpected value that is not equal to the original value. This value may be required as an index into a buffer, a loop iterator, or simply necessary state data. In any case, the value cannot be trusted and the system will be in an undefined state. While this method may be employed viably to isolate the low bits of a value, this usage is rare, and truncation usually implies that an implementation error has occurred.

Skutki

• Integrity

  Modify Memory

  The true value of the data is lost and corrupted data is used.

Zapobieganie

• Implementation

  Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.

Przykłady podatności

• CVE-2020-17087 Chain: integer truncation (CWE-197) causes small buffer allocation (CWE-131) leading to out-of-bounds write (CWE-787) in kernel pool, as exploited in the wild per CISA KEV.
• CVE-2009-0231 Integer truncation of length value leads to heap-based buffer overflow.
• CVE-2008-3282 Size of a particular type changes for 64-bit platforms, leading to an integer truncation in document processor causes incorrect index to be generated.

Słabość nadrzędna

• CWE-681 Incorrect Conversion between Numeric Types

Może też być

• CWE-195 Signed to Unsigned Conversion Error
• CWE-196 Unsigned to Signed Conversion Error
• CWE-192 Integer Coercion Error
• CWE-194 Unexpected Sign Extension

Kiedy powstaje

• Implementation

Dotyczy

C, C++, Java, C#

Uwagi

This weakness has traditionally been under-studied and under-reported, although vulnerabilities in popular software have been published in 2008 and 2009.

Źródła

1. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 6, "Truncation", Page 259, Addison Wesley, 2006