CVE-2026-93635 in Collaboration Suite
Summary
by MITRE • 10/14/2026
LDAP filter injection in Zimbra Collaboration Suite 10.1.0 through 10.1.21 allows unauthenticated attackers to alter external LDAP search filters. On domains using search-filter authentication and lazy provisioning, this creates a password oracle for external directory users. Authenticated S/MIME lookups can also return certificates and identity data for unintended directory entries.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in Zimbra Collaboration Suite versions 10.1.0 through 10.1.21 represents a critical LDAP filter injection flaw that fundamentally compromises the integrity of authentication mechanisms and sensitive data retrieval processes within the platform. This security defect arises from insufficient validation or sanitization of user-supplied input when constructing Lightweight Directory Access Protocol (LDAP) search queries. In standard software architecture, LDAP filters are used to query directory services for specific attributes such as usernames, email addresses, or certificate identifiers. When an application fails to properly escape special characters or restrict the scope of these inputs, attackers can inject maliciously crafted filter components into the query string. This injection allows unauthenticated actors to manipulate the logic of the search operation, effectively bypassing intended access controls and altering the results returned by the directory server.
The operational impact of this vulnerability is severe due to its potential for creating a password oracle effect on domains configured with specific authentication modes. Specifically, environments utilizing search-filter based authentication combined with lazy provisioning are at heightened risk. In such configurations, the system attempts to locate user accounts in an external LDAP directory by searching for attributes like email addresses or usernames before attempting to authenticate them against stored credentials. By injecting crafted filters, an attacker can determine whether a specific account exists in the external directory without needing valid credentials. This capability transforms the authentication endpoint into a timing-based or error-based oracle, allowing attackers to enumerate valid user accounts systematically. Once valid identities are established, these accounts become susceptible to brute-force attacks or credential stuffing, significantly lowering the barrier for unauthorized access.
Furthermore, the vulnerability extends beyond authentication bypass to include significant privacy and data leakage risks through authenticated S/MIME lookups. Even when an attacker possesses valid credentials for a lower-privilege account, they can exploit this flaw during Secure/Multipurpose Internet Mail Extensions (S/MIME) certificate retrieval operations. By manipulating the LDAP filter used to locate certificates associated with specific email addresses or identities, attackers can retrieve digital certificates and identity data belonging to unintended directory entries. This leakage exposes sensitive personal information, including full names, organizational units, and potentially other metadata linked to user profiles. The exposure of such data facilitates social engineering attacks, reputation damage for affected individuals, and provides additional context that could aid in more sophisticated targeted attacks against the organization's infrastructure.
From a classification perspective, this vulnerability aligns with CWE-90, which denotes Improper Neutralization of Special Elements used in an SQL Command, commonly referred to as LDAP Injection. The core issue lies in the failure to properly neutralize special elements that have meaning within the LDAP query syntax, allowing them to alter the intended command structure. Additionally, this flaw supports several tactics outlined in the MITRE ATT&CK framework. It directly enables T1078, Valid Accounts, by facilitating the discovery and exploitation of legitimate credentials through enumeration. The ability to retrieve unintended data also relates to T1213, Data from Information Repositories, as it allows for the extraction of sensitive information stored within the directory service without proper authorization checks.
Mitigation strategies must focus on immediate patching and architectural hardening. Organizations running Zimbra Collaboration Suite versions 10.1.0 through 10.1.21 should apply vendor-provided security patches immediately to address the input validation deficiencies in LDAP query construction. For environments where patching is not instantly feasible, temporary mitigations include restricting network access to the authentication endpoints and disabling lazy provisioning if it is not strictly required for business operations. Implementing strict input validation at the application layer to ensure that all user-supplied data used in LDAP filters is properly escaped or parameterized can also reduce risk. Additionally, monitoring logs for anomalous patterns of directory lookups, particularly those involving high volumes of failed searches or unusual attribute retrievals, can help detect exploitation attempts early. Long-term remediation should involve reviewing authentication configurations to minimize reliance on external directory lookups that are susceptible to injection and ensuring that S/MIME lookup mechanisms enforce strict access controls based on the requesting user's identity rather than just their ability to perform a search.