CVE-2018-18645 in Community Edition
Summary
by MITRE
An issue was discovered in GitLab Community and Enterprise Edition before 11.2.7, 11.3.x before 11.3.8, and 11.4.x before 11.4.3. It allows for Information Exposure via unsubscribe links in email replies.
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Analysis
by VulDB Data Team • 06/13/2023
This vulnerability exists in GitLab Community and Enterprise Edition versions prior to specific patch releases, creating a significant information exposure risk through email reply mechanisms. The flaw manifests when users receive notification emails containing unsubscribe links that inadvertently expose sensitive information about the system's internal state and user configurations. The vulnerability specifically affects versions before 11.2.7, 11.3.8, and 11.4.3 respectively, indicating a widespread impact across multiple release branches. The security issue stems from improper handling of email unsubscribe functionality where the system generates links containing identifiable information about project memberships, user permissions, and system configurations that could be exploited by malicious actors.
The technical implementation of this vulnerability involves the email notification system's processing of reply operations where unsubscribe links are constructed with insufficient sanitization of internal identifiers and user context data. When users reply to GitLab notifications, the system generates unsubscribe links that contain serialized data or direct references to internal system structures. This information exposure occurs because the unsubscribe mechanism does not properly obscure or encode sensitive parameters that would normally be hidden from end users. The flaw represents a classic case of insufficient input validation and output encoding, where internal system identifiers are directly exposed in externally visible URLs without proper security controls.
The operational impact of this vulnerability extends beyond simple information disclosure as it provides attackers with valuable reconnaissance data that could facilitate more sophisticated attacks. An attacker who intercepts or gains access to these unsubscribe links could potentially determine project membership, user roles, and system configuration details that would normally be protected within the GitLab environment. This information exposure could enable targeted attacks against specific projects or users, allowing threat actors to craft more convincing social engineering attempts or identify potential attack vectors within the system. The vulnerability aligns with CWE-200, which addresses information exposure, and could potentially support techniques described in the ATT&CK framework under reconnaissance and initial access phases.
Organizations using affected GitLab versions should immediately implement the recommended patches to address this vulnerability and prevent unauthorized information disclosure. The mitigation strategy involves upgrading to the patched versions 11.2.7, 11.3.8, and 11.4.3 respectively, which contain proper sanitization of unsubscribe link parameters. Additionally, administrators should review email notification settings and consider implementing additional monitoring for suspicious email activity patterns. Security teams should also conduct thorough audits of email communication systems to identify any other potential information exposure vulnerabilities in similar notification mechanisms. The vulnerability demonstrates the importance of proper parameter handling in web applications and the need for comprehensive security testing of notification systems that interact with external users.