CVE-2026-103547 in OpenBSD
Summary
by MITRE • 09/30/2026
In ldapd in OpenBSD 7.8 before errata 057 and 7.9 before errata 021, delegated BSD authentication results are correlated only by the LDAP child process client file descriptor and LDAP message ID. After a connection closes, a later connection that reuses the same file descriptor and message ID can receive the earlier authentication result. A remote attacker who can reach ldapd can complete a Bind as another identity. A missing connection can also cause a NULL pointer dereference. (ldapd is not enabled by default.)
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability in OpenBSD's ldapd service, specifically affecting versions prior to errata 057 for version 7.8 and errata 021 for version 7.9, represents a critical flaw in how the daemon manages session state during BSD authentication delegation. The core technical issue stems from an insufficient correlation mechanism between incoming LDAP requests and their corresponding asynchronous authentication results. Instead of maintaining strict isolation based on unique connection identifiers or cryptographic nonces, ldapd relies solely on the reuse of file descriptors and message IDs to map responses back to clients. This design choice creates a race condition window where state leakage can occur if connections are closed and reopened rapidly enough that system-level resource allocation reuses previous identifiers.
When an LDAP client establishes a connection with the daemon, it sends authentication requests identified by specific message IDs over allocated file descriptors. Upon completion of the delegated BSD authentication process, ldapd returns the result to the client associated with those identifiers. However, if the original TCP connection is closed and subsequently reopened, or if multiple connections are managed in a way that allows for identifier recycling before all pending results have been processed, there is no guarantee that the new connection's message ID will not match an outstanding request from a previous session. Consequently, when the authentication result arrives, ldapd delivers it to whichever client currently holds the matching file descriptor and message ID combination, regardless of whether that client initiated the original request or has any legitimate association with the pending operation.
This logic error enables a severe security impact classified under CWE-362: Concurrent Execution Using Shared Resource with Improper Synchronization of Referenced Resources. A remote attacker who can establish network connectivity to the ldapd service can exploit this state leakage by carefully timing connection closures and reconnections to hijack authentication results intended for other users. By doing so, an attacker can effectively perform a Bind operation as another identity without possessing valid credentials for that account. This constitutes CWE-287: Improper Authentication, allowing unauthorized access to directory services and potentially leading to privilege escalation or data exfiltration depending on the permissions associated with the hijacked identity.
Beyond authentication bypass, the vulnerability also introduces stability risks through a NULL pointer dereference scenario. If a connection closes unexpectedly while an authentication result is still pending in the queue but no new client has yet reused the specific file descriptor and message ID combination to claim it, ldapd may attempt to deliver the response to a null or invalid context. This results in a service crash, contributing to CWE-476: NULL Pointer Dereference and impacting availability by causing denial of service conditions for legitimate users relying on the directory services hosted by ldapd.
Mitigation strategies primarily involve applying the official errata updates provided by OpenBSD, which correct the internal state management logic to ensure unique session tracking independent of transient resource identifiers such as file descriptors. Until patches are applied, administrators should consider disabling ldapd if it is not strictly required for their infrastructure, noting that the service is disabled by default in standard configurations. Additionally, implementing network-level access controls via firewalls or ACLs can restrict exposure to trusted subnets only, reducing the attack surface available to remote adversaries attempting to exploit this race condition. Monitoring logs for unusual patterns of connection churn and authentication failures may also aid in early detection of exploitation attempts targeting this flaw.