CVE-2021-29923 in TimesTen In-Memory Database
Summary
by MITRE • 08/08/2021
Go before 1.17 does not properly consider extraneous zero characters at the beginning of an IP address octet, which (in some situations) allows attackers to bypass access control that is based on IP addresses, because of unexpected octal interpretation. This affects net.ParseIP and net.ParseCIDR.
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Analysis
by VulDB Data Team • 05/21/2025
The vulnerability described in CVE-2021-29923 represents a critical flaw in the go programming language's network parsing functionality that stems from improper handling of leading zero characters in IP address octets. This issue affects all versions of go prior to 1.17 and specifically impacts the net.ParseIP and net.ParseCIDR functions within the standard library. The core problem arises when IP addresses contain leading zeros in their octet representations, which should be interpreted as decimal numbers but are instead processed as octal values due to Go's implicit conversion behavior. This misinterpretation creates a fundamental security gap in access control mechanisms that rely on IP address validation, as attackers can exploit this quirk to craft malicious IP addresses that bypass network restrictions.
The technical implementation of this vulnerability exploits the difference between decimal and octal number systems in Go's parsing logic. When a string containing an IP address with leading zeros is processed by net.ParseIP or net.ParseCIDR, the parser interprets octets beginning with zero as octal numbers rather than decimal values. For example, the IP address 192.168.010.1 would be interpreted as 192.168.8.1 because 010 in octal equals 8 in decimal. This behavior occurs because Go's parser treats any numeric string beginning with zero as potentially octal, even when the context clearly indicates a decimal IP address. The flaw is particularly insidious because it can be leveraged to bypass firewall rules, authentication systems, or other network-based access controls that depend on IP address validation, creating a vector for privilege escalation or unauthorized access to protected resources.
The operational impact of this vulnerability extends beyond simple network access bypasses and can compromise entire security infrastructures that rely on IP-based restrictions. Systems implementing IP whitelisting, VPN access controls, or network segmentation may be rendered ineffective against attackers who understand and exploit this parsing inconsistency. The vulnerability affects a wide range of applications including web servers, network monitoring tools, and security appliances that depend on Go's standard library for IP address validation. Attackers can craft IP addresses that appear legitimate to access control systems while actually representing different network locations, effectively allowing them to circumvent security controls designed to restrict access based on IP address ranges. This vulnerability particularly affects applications deployed in environments where network security is maintained through IP-based filtering mechanisms, making it a significant concern for enterprise security architectures.
Organizations should immediately upgrade to Go version 1.17 or later to address this vulnerability, as the fix involves proper handling of leading zero characters in IP address parsing to ensure consistent decimal interpretation. Additionally, security teams should conduct comprehensive audits of all Go applications that utilize net.ParseIP or net.ParseCIDR functions to identify potential exposure to this vulnerability. Network administrators should review existing access control policies and IP-based restrictions to ensure they are not susceptible to this type of attack vector. The vulnerability aligns with CWE-1288, which addresses improper handling of leading zeros in numeric parsing, and represents a specific instance of the broader ATT&CK technique T1078.101, which involves valid accounts and legitimate credentials. Organizations should also implement network monitoring to detect anomalous IP address patterns that might indicate exploitation attempts, and consider additional validation layers beyond simple IP address parsing to prevent exploitation of this class of vulnerability.