CVE-2026-104034 in SSSD
Summary
by MITRE • 10/06/2026
A flaw was found in SSSD. A use-after-free vulnerability exists in the Kerberos Credential Manager (KCM) responder during Kerberos ticket-granting ticket (TGT) renewal, where a deferred callback accesses memory that has already been released. An authenticated local user with a renewable Kerberos ticket can trigger this issue on systems configured with KCM renewal, causing the KCM responder service to crash and resulting in a Denial of Service (DoS).
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Analysis
by VulDB Data Team • 10/06/2026
The vulnerability identified within the System Security Services Daemon involves a critical memory management error located specifically within its Kerberos Credential Manager responder component. This flaw manifests as a use-after-free condition, which occurs when software continues to access or reference a block of memory after it has been freed back to the system allocator. In this specific instance, the defect is triggered during the process of renewing a Kerberos Ticket-Granting Ticket. The underlying technical mechanism involves a deferred callback function that attempts to interact with data structures associated with the ticket renewal operation. However, due to improper lifecycle management or race conditions in memory handling, these data structures have already been deallocated by another part of the system before this delayed execution context runs. When the callback executes and dereferences pointers pointing to this freed memory region, it results in undefined behavior that typically leads to a segmentation fault or immediate termination of the process.
From an operational perspective, this vulnerability poses a significant risk to systems configured with KCM renewal enabled. The primary impact is a Denial of Service against the SSSD service itself. Because the Kerberos Credential Manager responder crashes upon encountering this memory corruption, any user session relying on that specific instance for authentication or ticket management will be disrupted. While the initial trigger requires an authenticated local user possessing a renewable Kerberos ticket, the consequence is not direct code execution but rather the destabilization of the identity service infrastructure. This can lead to intermittent connectivity issues, failed login attempts, and potential disruption of services that depend on continuous SSSD availability for authentication lookups or credential caching. In environments where high availability is critical, such as enterprise domains with strict uptime requirements, repeated exploitation by multiple users could effectively render the system unable to authenticate new requests until the service is manually restarted.
This vulnerability aligns closely with Common Weakness Enumeration identifier CWE-416, which describes use-after-free errors resulting from improper memory management practices. The attack vector falls under ATT&CK technique T1078, specifically relating to valid accounts and authentication bypass or disruption, although in this case the focus is on availability rather than privilege escalation. An attacker with local access can exploit this by manipulating ticket renewal timers or triggering specific Kerberos operations that force the system into the vulnerable state where the deferred callback executes after memory release. The severity of this issue is compounded by its location within a core authentication component, meaning that compromising the stability of SSSD directly impacts the security posture and operational continuity of the host machine.
Mitigation strategies should prioritize applying vendor-provided patches that address the memory lifecycle issues within the KCM responder codebase. Administrators must ensure that all systems running affected versions of SSSD are updated to a version where this use-after-free condition has been resolved through proper pointer nullification or refcounting adjustments before callback execution. In scenarios where immediate patching is not feasible, restricting local user privileges and limiting the ability to request Kerberos ticket renewals can reduce the attack surface. Additionally, monitoring system logs for unexpected SSSD process restarts or segmentation faults can serve as an early warning indicator of exploitation attempts. Regular auditing of authentication services and ensuring that renewable tickets are managed with strict timeout policies can also help minimize the window of opportunity for triggering this specific memory corruption flaw.