CVE-2026-104039 in Red Hat
Summary
by MITRE • 10/06/2026
A flaw was found in SSSD. A local user can cause a denial of service (DoS) by disrupting system authentication services. When handling Generic Security Services Application Programming Interface (GSSAPI) authentication in the Pluggable Authentication Module (PAM) responder, cached connection state is freed upon completion without clearing the reference pointer. An attacker can exploit this by sending an additional request over the same connection, causing the service to access invalid memory and unexpectedly terminate.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/06/2026
The vulnerability identified within System Security Services Daemon represents a critical flaw in how the application manages resource lifecycle during authentication processes involving Generic Security Services Application Programming Interface protocols. Specifically, the defect resides within the Pluggable Authentication Module responder component of SSSD when it handles GSSAPI-based authentications. The core technical issue is a use-after-free condition where cached connection state memory is deallocated immediately upon the completion of an authentication transaction. However, the pointer referencing this allocated memory block is not nullified or cleared before being returned to the application's internal management structures. This oversight leaves a dangling reference that remains valid within the program's logic but points to freed heap space, creating a window for exploitation by any local user who can interact with the SSSD service interface.
From an operational perspective, this flaw allows a malicious actor with local system access to trigger a denial of service against critical authentication infrastructure. By sending a subsequent request over the same connection immediately after completing an initial GSSAPI authentication sequence, the attacker forces the daemon to attempt accessing or manipulating memory that has already been released by the operating system's allocator. This invalid memory access typically results in segmentation faults or similar fatal errors within the SSSD process. Since SSSD is often responsible for managing identity and authentication services across Linux environments, particularly those integrated with Active Directory or other directory services, its unexpected termination can disrupt login capabilities for all users relying on that specific daemon instance. This effectively creates a localized denial of service where legitimate administrators and users are unable to authenticate to the system until the service is manually restarted by an administrator with higher privileges.
The classification of this vulnerability aligns closely with Common Weakness Enumeration identifier CWE-416, which describes use after free errors. These types of memory management bugs are particularly dangerous because they can lead not only to crashes but potentially to arbitrary code execution if the freed memory is reallocated and overwritten by an attacker before being accessed again. Although in this specific instance the primary impact observed is a denial of service due to immediate termination, the underlying mechanism remains consistent with CWE-416 standards. Furthermore, from a tactical standpoint within the MITRE ATT&CK framework, this vulnerability facilitates Local Privilege Escalation or Denial of Service via component manipulation (T1530). An attacker leveraging this flaw does not need elevated privileges to initiate the attack but can significantly degrade system availability and potentially create conditions for further exploitation if the memory layout allows it.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary solution is to apply vendor-provided patches that update SSSD to versions where this specific use-after-free condition has been corrected by properly nullifying pointers after deallocation or implementing reference counting mechanisms to ensure memory is only freed when no active references remain. System administrators should monitor for updates from their respective Linux distribution vendors and prioritize patching systems running vulnerable versions of SSSD, especially those exposed to untrusted local users such as in multi-tenant environments or public-facing servers with shell access. Additionally, implementing strict file permissions on the sockets used by SSSD can limit which local users are able to initiate GSSAPI authentication requests, thereby reducing the attack surface available to potential exploiters until patches are applied. Regular auditing of system logs for unexpected service restarts can also help in detecting attempted exploitation activities early.