CVE-2026-104733 in ejabberd
Summary
by MITRE • 10/02/2026
User Impersonation in ProcessOnes XMMP Server ejabberd <= 26.04 allows an attacker to impersonate arbitrary users via unvalidated authzid parameter in SASL-PLAIN mechanism.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/02/2026
The vulnerability identified within the ProcessOne XMPP server, specifically affecting versions of ejabbered up through and including version 26.04, represents a critical authentication bypass flaw rooted in improper validation of session parameters during the Simple Authentication and Security Layer process. This issue allows an authenticated attacker to impersonate arbitrary users on the network by exploiting the lack of rigorous checks on the authorization identity parameter sent during the SASL-PLAIN mechanism handshake. In standard XMPP operations, when a client connects to the server, it initiates authentication using credentials such as username and password. The server then validates these credentials against its user database. Upon successful validation, the session is established with an associated account identifier. However, in this specific implementation flaw, the server fails to verify that the authorization identity requested by the client actually matches the authenticated principal or exists within the allowed scope for that connection. This oversight creates a significant gap between authentication and authorization, allowing malicious actors to decouple their actual login credentials from the identity they wish to assume on the network.
From a technical perspective, the flaw resides in how the ejabberd server processes the authzid field during the SASL negotiation phase. The Simple Authentication and Security Layer is designed to provide authentication and optional authorization services for Internet protocols. During this process, clients may request an authorization identity different from their login name, which can be legitimate in scenarios involving service accounts or proxying. However, ejabberd versions prior to 26.04 do not adequately validate whether the requesting client has permission to assume that specific target identity. Consequently, if an attacker possesses valid credentials for any user account on the server, they can manipulate the SASL-PLAIN exchange to specify a different username in the authorization request field. The server accepts this request without verifying ownership or permissions, thereby granting the attacker full access and privileges associated with the impersonated victim's account. This behavior violates fundamental security principles regarding identity management and trust boundaries within distributed messaging systems.
The operational impact of this vulnerability is severe, as it effectively nullifies the integrity of user authentication on affected XMPP servers. An adversary who exploits this flaw can gain unauthorized access to sensitive communications, personal data, and administrative functions belonging to any other user on the same server instance. This capability facilitates a range of malicious activities including social engineering attacks where messages appear to originate from trusted individuals or entities, leading to potential phishing campaigns or reputation damage for victims. Furthermore, if the impersonated account holds elevated privileges such as those associated with bot management rooms or administrative roles, the attacker could escalate their access further, potentially compromising entire server configurations or other connected clients through malicious commands sent under false pretenses. The ability to seamlessly inject messages into ongoing conversations also undermines trust in real-time communication platforms that rely on identity verification for secure collaboration.
This vulnerability aligns with Common Weakness Enumeration category CWE-287, which describes Improper Authentication, specifically relating to the failure to properly verify credentials or authorization contexts during session establishment. It also maps closely to MITRE ATT&CK technique T1078, Valid Accounts, where adversaries use legitimate system accounts to maintain access and evade detection by blending in with normal network traffic. The exploitation of this flaw does not require complex binary manipulation or memory corruption techniques but rather relies on logical errors within the application layer protocol handling, making it relatively straightforward for attackers with basic knowledge of XMPP protocols to execute successfully against unpatched systems.
To mitigate this risk, administrators must immediately upgrade ejabberd to version 26.04 or later where these validation checks have been corrected and strengthened. In addition to patching the software, organizations should enforce strict access control policies that limit which users are permitted to request authorization identities different from their login names unless explicitly required for specific service functions. Implementing multi-factor authentication adds an additional layer of security by ensuring that even if credentials are compromised, unauthorized impersonation attempts can be detected and blocked through secondary verification steps. Regular auditing of server logs for anomalous SASL negotiation patterns can also help in identifying potential exploitation attempts before significant damage occurs. Maintaining up-to-date software configurations is essential to closing gaps between authentication mechanisms and actual authorization enforcement within enterprise communication infrastructures.