CVE-2015-3900 in RubyGems
Summary
by MITRE
RubyGems 2.0.x before 2.0.16, 2.2.x before 2.2.4, and 2.4.x before 2.4.7 does not validate the hostname when fetching gems or making API request, which allows remote attackers to redirect requests to arbitrary domains via a crafted DNS SRV record, aka a "DNS hijack attack."
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability described in CVE-2015-3900 represents a critical security flaw in RubyGems, a widely used package management system for ruby applications. This issue affects multiple versions of the RubyGems library across its 2.0.x, 2.2.x, and 2.4.x release lines, specifically before the mentioned patch versions. The core problem lies in the improper validation of hostnames during network operations, creating a pathway for malicious actors to manipulate network traffic through DNS resolution. This vulnerability directly impacts the integrity and security of ruby application dependencies and can lead to significant operational risks for systems relying on ruby gem installations.
The technical flaw manifests when RubyGems processes API requests or gem downloads without properly validating the hostname information returned from DNS queries. In particular, the system fails to validate SRV (Service) records, which are DNS records that specify the location of services for a domain. Attackers can exploit this weakness by crafting malicious DNS SRV records that redirect requests to attacker-controlled domains instead of the legitimate gem servers. This allows for man-in-the-middle attacks where network traffic intended for official ruby gem repositories gets redirected to malicious servers controlled by adversaries. The vulnerability operates at the network layer where DNS resolution occurs, making it particularly dangerous as it can be exploited without requiring authentication or elevated privileges.
The operational impact of this vulnerability extends beyond simple request redirection, creating potential for data theft, code injection, and supply chain attacks. When developers install gems through affected RubyGems versions, their systems become vulnerable to attacks that can compromise the integrity of downloaded packages. An attacker could potentially serve malicious versions of popular gems, leading to compromised applications and systems. This vulnerability also enables broader attack scenarios where adversaries might redirect traffic to phishing servers or use the redirection to establish persistence within target networks. The DNS hijack attack vector represents a sophisticated method of attack that leverages fundamental DNS infrastructure weaknesses to compromise software supply chains, affecting organizations of all sizes that depend on ruby applications and package management.
Organizations should immediately update their RubyGems installations to versions 2.0.16, 2.2.4, or 2.4.7, depending on their current version, to mitigate this vulnerability. System administrators should also implement network monitoring to detect unusual DNS resolution patterns and traffic redirection attempts. Additional mitigations include configuring DNS servers to prevent unauthorized SRV record modifications and implementing network segmentation to limit the attack surface. The vulnerability aligns with CWE-20, which describes improper input validation, and maps to ATT&CK technique T1190, DNS Tunneling, as it exploits DNS infrastructure for malicious purposes. Security teams should also consider implementing certificate pinning for gem repositories and monitoring for unauthorized gem installations that could indicate exploitation attempts. This vulnerability highlights the critical importance of proper hostname validation in network operations and demonstrates how seemingly minor implementation flaws can create significant security risks in software supply chain management.