CWE - CWE-1335: Incorrect Bitwise Shift of Integer (4.14)

Weakness ID: 1335

Vulnerability Mapping: ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities
Abstraction: BaseBase - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.

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Description

An integer value is specified to be shifted by a negative amount or an amount greater than or equal to the number of bits contained in the value causing an unexpected or indeterminate result.

Extended Description

Specifying a value to be shifted by a negative amount is undefined in various languages. Various computer architectures implement this action in different ways. The compilers and interpreters when generating code to accomplish a shift generally do not do a check for this issue.

Specifying an over-shift, a shift greater than or equal to the number of bits contained in a value to be shifted, produces a result which varies by architecture and compiler. In some languages, this action is specifically listed as producing an undefined result.

Relationships

This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

Relevant to the view "Research Concepts" (CWE-1000)

Nature	Type	ID	Name
ChildOf	Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things.	682	Incorrect Calculation

Relevant to the view "Software Development" (CWE-699)

Nature	Type	ID	Name
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	189	Numeric Errors

Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Phase	Note
Implementation	Adding shifts without properly verifying the size and sign of the shift amount.

Applicable Platforms

This listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

C (Undetermined Prevalence)

C++ (Undetermined Prevalence)

C# (Undetermined Prevalence)

Java (Undetermined Prevalence)

JavaScript (Undetermined Prevalence)

Operating Systems

Class: Not OS-Specific (Undetermined Prevalence)

Technologies

Class: Not Technology-Specific (Undetermined Prevalence)

Common Consequences

This table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Scope	Impact	Likelihood
Integrity	Technical Impact: DoS: Crash, Exit, or Restart

Demonstrative Examples

Example 1

A negative shift amount for an x86 or x86_64 shift instruction will produce the number of bits to be shifted by taking a 2's-complement of the shift amount and effectively masking that amount to the lowest 6 bits for a 64 bit shift instruction.

(bad code)

Example Language: C

unsigned int r = 1 << -5;

The example above ends up with a shift amount of -5. The hexadecimal value is FFFFFFFFFFFFFFFD which, when bits above the 6th bit are masked off, the shift amount becomes a binary shift value of 111101 which is 61 decimal. A shift of 61 produces a very different result than -5. The previous example is a very simple version of the following code which is probably more realistic of what happens in a real system.

(bad code)

Example Language: C

int choose_bit(int reg_bit, int bit_number_from_elsewhere)
{

if (NEED_TO_SHIFT)
{

reg_bit -= bit_number_from_elsewhere;

}
return reg_bit;

}
unsigned int handle_io_register(unsigned int *r)
{

unsigned int the_bit = 1 << choose_bit(5, 10);
*r |= the_bit;
return the_bit;

}

(good code)

Example Language: C

int choose_bit(int reg_bit, int bit_number_from_elsewhere)
{

if (NEED_TO_SHIFT)
{

reg_bit -= bit_number_from_elsewhere;

}
return reg_bit;

}

unsigned int handle_io_register(unsigned int *r)
{

int the_bit_number = choose_bit(5, 10);
if ((the_bit_number > 0) && (the_bit_number < 63))
{

unsigned int the_bit = 1 << the_bit_number;
*r |= the_bit;

}
return the_bit;

}

Note that the good example not only checks for negative shifts and disallows them, but it also checks for over-shifts. No bit operation is done if the shift is out of bounds. Depending on the program, perhaps an error message should be logged.

Observed Examples

Reference	Description
CVE-2009-4307	An unexpected large value in the ext4 filesystem causes an overshift condition resulting in a divide by zero.
CVE-2012-2100	An unexpected large value in the ext4 filesystem causes an overshift condition resulting in a divide by zero - fix of CVE-2009-4307.
CVE-2020-8835	An overshift in a kernel allowed out of bounds reads and writes resulting in a root takeover.
CVE-2015-1607	Program is not properly handling signed bitwise left-shifts causing an overlapping memcpy memory range error.
CVE-2016-9842	Compression function improperly executes a signed left shift of a negative integer.
CVE-2018-18445	Some kernels improperly handle right shifts of 32 bit numbers in a 64 bit register.
CVE-2013-4206	Putty has an incorrectly sized shift value resulting in an overshift.
CVE-2018-20788	LED driver overshifts under certain conditions resulting in a DoS.

Potential Mitigations

Phase: Implementation

Implicitly or explicitly add checks and mitigation for negative or over-shift values.

Memberships

This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.

Nature	Type	ID	Name
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1408	Comprehensive Categorization: Incorrect Calculation

Vulnerability Mapping Notes

Usage: ALLOWED

(this CWE ID could be used to map to real-world vulnerabilities)

Reason: Acceptable-Use

Rationale:

This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.

Comments:

Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Content History

Submissions
Submission Date	Submitter	Organization
2021-03-29 (CWE 4.5, 2021-07-20)	CWE Content Team	MITRE
2021-03-29 (CWE 4.5, 2021-07-20)
Modifications
Modification Date	Modifier	Organization
2022-10-13	CWE Content Team	MITRE
2022-10-13	updated Demonstrative_Examples, Observed_Examples
2023-04-27	CWE Content Team	MITRE
2023-04-27	updated Relationships
2023-06-29	CWE Content Team	MITRE
2023-06-29	updated Mapping_Notes


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Common Weakness Enumeration

CWE-1335: Incorrect Bitwise Shift of Integer

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