CVE-2018-3822 in X-Pack Security
Summary
by MITRE
X-Pack Security versions 6.2.0, 6.2.1, and 6.2.2 are vulnerable to a user impersonation attack via incorrect XML canonicalization and DOM traversal. An attacker might have been able to impersonate a legitimate user if the SAML Identity Provider allows for self registration with arbitrary identifiers and the attacker can register an account which an identifier that shares a suffix with a legitimate account. Both of those conditions must be true in order to exploit this flaw.
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Analysis
by VulDB Data Team • 02/06/2021
The vulnerability described in CVE-2018-3822 represents a critical user impersonation flaw within X-Pack Security components of Elasticsearch versions 6.2.0 through 6.2.2. This security weakness stems from improper handling of XML canonicalization and DOM traversal during SAML authentication processes, creating a pathway for malicious actors to exploit legitimate user identities. The vulnerability specifically targets the SAML authentication mechanism that Elasticsearch uses to integrate with external identity providers, making it particularly dangerous in enterprise environments where SAML-based single sign-on is commonly deployed.
The technical implementation flaw occurs when the system processes SAML assertions containing user identifiers that share common suffixes with legitimate accounts. During XML canonicalization, the system fails to properly validate or sanitize the identifier strings, allowing attackers to manipulate the DOM traversal logic in ways that can cause the system to incorrectly map an attacker-controlled identifier to a legitimate user account. This type of vulnerability falls under CWE-20, which encompasses improper input validation, and specifically relates to CWE-121, which deals with buffer overflow conditions, though the manifestation here is more subtle and involves identifier mapping rather than direct memory corruption. The vulnerability demonstrates a classic case of insufficient sanitization of user-supplied data within authentication contexts, creating a path for privilege escalation through identity spoofing.
The operational impact of this vulnerability extends beyond simple authentication bypass, as it enables attackers to gain unauthorized access to systems with elevated privileges. When combined with the requirement that the SAML Identity Provider must allow self-registration with arbitrary identifiers, this creates a two-pronged attack vector that requires both the technical exploitation of the XML processing flaw and the ability to register accounts with malicious identifiers. This attack scenario aligns with ATT&CK technique T1078.004, which covers valid accounts obtained through compromise, and demonstrates how flaws in authentication processing can be leveraged to achieve persistent access. The vulnerability particularly affects organizations that rely on SAML-based authentication and have configured their identity providers to allow flexible user registration, as the attack requires both the specific software flaw and the appropriate environmental conditions to be present.
Organizations should immediately upgrade to Elasticsearch versions that address this vulnerability, specifically those beyond 6.2.2, where the XML canonicalization and DOM traversal processing has been corrected. The mitigation strategy must include both software patching and operational controls to prevent attackers from registering malicious accounts, as well as monitoring for unusual SAML assertion patterns that might indicate exploitation attempts. Security teams should also implement additional authentication controls such as multi-factor authentication and enhanced monitoring of user access patterns to detect potential impersonation attempts. The vulnerability highlights the importance of proper input validation in security-critical code paths and demonstrates how seemingly minor flaws in XML processing can have significant implications for authentication security. Regular security assessments of identity provider configurations and SAML implementation should be conducted to ensure that environments are not inadvertently configured to allow the conditions necessary for this attack to succeed.