CVE-2018-3759 in private_address_check Ruby Gem
Summary
by MITRE
private_address_check ruby gem before 0.5.0 is vulnerable to a time-of-check time-of-use (TOCTOU) race condition due to the address the socket uses not being checked. DNS entries with a TTL of 0 can trigger this case where the initial resolution is a public address but the subsequent resolution is a private address.
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Analysis
by VulDB Data Team • 03/27/2023
The vulnerability described in CVE-2018-3759 affects the private_address_check ruby gem version 0.5.0 and earlier, presenting a significant time-of-check time-of-use race condition that can be exploited to bypass security controls. This flaw specifically targets the gem's handling of network address validation, where the system performs an initial DNS resolution check followed by a subsequent verification that can be manipulated through DNS cache poisoning or timing attacks. The vulnerability stems from the gem's failure to properly validate that the address resolved during the second check matches the address resolved during the first check, creating a window where malicious actors can exploit this temporal discrepancy. The security implications are particularly severe because the gem is designed to verify whether network addresses are private or public, a critical function for network security applications that rely on such checks to enforce access controls and prevent unauthorized connections to internal systems.
The technical exploitation of this vulnerability occurs when DNS entries with a TTL of zero are present in the system's DNS cache or when DNS resolution is manipulated during the brief window between the initial check and the subsequent use of the address. During this race condition, the first DNS resolution returns a public IP address, which passes the initial validation check, but when the system subsequently attempts to use that address for network operations, the DNS cache has been updated with a private IP address that would have failed validation had the system performed a fresh lookup. This type of vulnerability falls under CWE-367 which specifically addresses Time-of-Check to Time-of-Use race conditions, where an attacker can manipulate system state between a validation check and the actual use of the validated resource. The flaw represents a classic example of how seemingly innocuous network validation logic can be subverted through timing attacks and DNS manipulation techniques that are well-documented in security literature and commonly used in advanced persistent threat operations.
The operational impact of this vulnerability extends beyond simple bypass of address validation checks, as it can enable attackers to gain unauthorized access to internal network resources that should be protected from external connections. Systems relying on the private_address_check gem for security enforcement may be vulnerable to attacks where malicious actors can craft DNS responses that initially appear to resolve to public addresses but subsequently resolve to private addresses within the critical race window. This vulnerability can be particularly dangerous in environments where network segmentation and access control policies depend on distinguishing between public and private IP addresses, as it effectively allows attackers to circumvent these protections. The attack vector is particularly concerning because it can be executed through standard DNS manipulation techniques, making it accessible to threat actors with moderate technical capabilities and requiring no specialized tools beyond basic network reconnaissance and DNS poisoning capabilities.
Organizations using affected versions of the private_address_check gem should immediately upgrade to version 0.5.0 or later, which addresses this race condition by implementing proper address validation that ensures consistency between the initial check and subsequent use of network addresses. The mitigation strategy should include implementing DNS security measures such as DNSSEC to prevent cache poisoning attacks that could be used to exploit this vulnerability, along with monitoring for unusual DNS resolution patterns that might indicate an attempt to manipulate the race condition. Security teams should also consider implementing network segmentation controls that do not rely solely on address validation for access control, as well as regular auditing of DNS cache behavior to detect potential manipulation attempts. From an ATT&CK framework perspective, this vulnerability maps to techniques such as T1071.004 for DNS tunneling and T1566 for credential access through social engineering, as attackers can leverage this flaw to bypass network security controls that depend on address validation. The vulnerability also relates to T1082 for system information discovery, as attackers can use it to gather information about internal network topology and access internal resources that should be protected from external access.