CVE-2019-18933 in Server
Summary
by MITRE
In Zulip Server versions from 1.7.0 to before 2.0.7, a bug in the new user signup process meant that users who registered their account using social authentication (e.g., GitHub or Google SSO) in an organization that also allows password authentication could have their personal API key stolen by an unprivileged attacker, allowing nearly full access to the user's account.
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Analysis
by VulDB Data Team • 02/26/2024
The vulnerability identified as CVE-2019-18933 represents a critical security flaw in Zulip Server versions ranging from 1.7.0 through the pre-2.0.7 releases, specifically affecting the user registration and authentication workflow. This issue stems from a design oversight in how the system handles accounts created through social authentication methods while simultaneously allowing traditional password-based authentication within the same organizational context. The flaw creates a pathway for privilege escalation and unauthorized access that directly impacts user account security and organizational data integrity.
The technical implementation of this vulnerability occurs during the account registration process when users authenticate through social providers such as GitHub or Google Single Sign-On services. The system's flawed logic fails to properly isolate or secure the API key generation and assignment process for social authentication users who subsequently attempt to access password-based login mechanisms. This cross-contamination of authentication paths creates an exploit vector where an attacker with minimal privileges can intercept and steal personal API keys from legitimate users. The vulnerability manifests as a race condition or improper access control during the account creation sequence, allowing unauthorized entities to gain access to authentication tokens that should remain restricted to the legitimate user.
The operational impact of this vulnerability extends beyond individual account compromise to potentially affect entire organizational security postures. When an unprivileged attacker successfully steals a user's personal API key, they gain near-complete access to the compromised account, including the ability to read messages, send communications, modify settings, and potentially escalate privileges within the system. This represents a significant breach of the principle of least privilege and undermines the security model of the authentication system. The vulnerability is particularly concerning because it affects users who may have legitimate access to sensitive organizational communications and data, making the compromise of their credentials a serious threat to information security.
This vulnerability aligns with CWE-284, which addresses improper access control, and demonstrates characteristics consistent with privilege escalation attacks documented in the MITRE ATT&CK framework under the privilege escalation tactic. The flaw essentially allows an attacker to move from a low-privilege state to one with extensive access rights through the exploitation of a design flaw in the authentication system. Organizations using affected Zulip Server versions face significant risk of data exfiltration, unauthorized communication, and potential lateral movement within their network infrastructure. The vulnerability is particularly dangerous in environments where social authentication is enabled alongside password authentication, as it creates an intersection point where security boundaries become compromised.
Mitigation strategies for this vulnerability require immediate patching to Zulip Server versions 2.0.7 and later, which contain the necessary code fixes to properly isolate authentication flows and prevent API key leakage between different authentication methods. Organizations should also implement additional monitoring for suspicious authentication patterns and API key usage, particularly when users transition from social to password-based authentication. Security teams should review and audit existing user accounts to identify potential compromise, enforce multi-factor authentication policies, and consider implementing stricter access controls for API key management. The fix addresses the root cause by ensuring proper isolation of authentication contexts and implementing robust access control mechanisms that prevent cross-contamination of authentication tokens between different registration pathways.