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.

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.

Primary

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

Integrity
DoS: Crash, Exit, or Restart

Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
High

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

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.

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.

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;

}

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.

CVE-2009-4307
An unexpected large value in the ext4 filesystem causes an overshift condition resulting in a divide by zero.
https://www.cve.org/CVERecord?id=CVE-2009-4307

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.
https://www.cve.org/CVERecord?id=CVE-2012-2100

CVE-2020-8835
An overshift in a kernel allowed out of bounds reads and writes resulting in a root takeover.
https://www.cve.org/CVERecord?id=CVE-2020-8835

CVE-2015-1607
Program is not properly handling signed bitwise left-shifts causing an overlapping memcpy memory range error.
https://www.cve.org/CVERecord?id=CVE-2015-1607

CVE-2016-9842
Compression function improperly executes a signed left shift of a negative integer.
https://www.cve.org/CVERecord?id=CVE-2016-9842

CVE-2018-18445
Some kernels improperly handle right shifts of 32 bit numbers in a 64 bit register.
https://www.cve.org/CVERecord?id=CVE-2018-18445

CVE-2013-4206
Putty has an incorrectly sized shift value resulting in an overshift.
https://www.cve.org/CVERecord?id=CVE-2013-4206

CVE-2018-20788
LED driver overshifts under certain conditions resulting in a DoS.
https://www.cve.org/CVERecord?id=CVE-2018-20788

Allowed
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.
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.

CWE Content Team
MITRE
2021-03-29
4.5
2021-07-20

CWE Content Team
MITRE
2022-10-13
updated Demonstrative_Examples, Observed_Examples

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Detection_Factors, Weakness_Ordinalities