CWE-1389

Incorrect Parsing of Numbers with Different Radices

Base

Incomplete

Description

The product parses numeric input assuming base 10 (decimal) values, but it does not account for inputs that use a different base number (radix).

{"xhtml:p":["Frequently, a numeric input that begins with \"0\" is treated as octal, or \"0x\" causes it to be treated as hexadecimal, e.g. by the inet_addr() function. For example, \"023\" (octal) is 35 decimal, or \"0x31\" is 49 decimal. Other bases may be used as well. If the developer assumes decimal-only inputs, the code could produce incorrect numbers when the inputs are parsed using a different base. This can result in unexpected and/or dangerous behavior. For example, a \"0127.0.0.1\" IP address is parsed as octal due to the leading \"0\", whose numeric value would be the same as 87.0.0.1 (decimal), where the developer likely expected to use 127.0.0.1.","The consequences vary depending on the surrounding code in which this weakness occurs, but they can include bypassing network-based access control using unexpected IP addresses or netmasks, or causing apparently-symbolic identifiers to be processed as if they are numbers. In web applications, this can enable bypassing of SSRF restrictions."]}

Parent Weaknesses (ChildOf)

CWE-704: Incorrect Type Conversion or C...

Common Consequences

Scope

Confidentiality

Impact

Read Application Data

Scope

Integrity

Impact

Bypass Protection Mechanism, Alter Execution Logic

Potential Mitigations

Implementation

If only decimal-based values are expected in the application, conditional checks should be created in a way that prevent octal or hexadecimal strings from being checked. This can be achieved by converting any numerical string to an explicit base-10 integer prior to the conditional check, to prevent octal or hex values from ever being checked against the condition.

Implementation

If various numerical bases do need to be supported, check for leading values indicating the non-decimal base you wish to support (such as 0x for hex) and convert the numeric strings to integers of the respective base. Reject any other alternative-base string that is not intentionally supported by the application.

Implementation

If regular expressions are used to validate IP addresses, ensure that they are bounded using ^ and $ to prevent base-prepended IP addresses from being matched.

CVE-2021-29662

Chain: Use of zero-prepended IP addresses in Perl-based IP validation module can lead to an access control bypass.

CVE-2021-28918

Chain: Use of zero-prepended IP addresses in a product that manages IP blocks can lead to an SSRF.

CVE-2021-29921

Chain: Use of zero-prepended IP addresses in a Python standard library package can lead to an SSRF.

CVE-2021-29923

Chain: Use of zero-prepended IP addresses in the net Golang library can lead to an access control bypass.

CVE-2021-29424

Chain: Use of zero-prepended IP addresses in Perl netmask module allows bypass of IP-based access control.

CVE-2016-4029

Chain: incorrect validation of intended decimal-based IP address format (CWE-1286) enables parsing of octal or hexadecimal formats (CWE-1389), allowing bypass of an SSRF protection mechanism (CWE-918).

CVE-2020-13776

Mishandling of hex-valued usernames leads to unexpected decimal conversion and privilege escalation in the systemd Linux suite.