CVE-2026-104038 in Red Hat
Summary
by MITRE • 10/06/2026
A flaw was found in sssd. A remote attacker can cause a denial of service (DoS) by submitting a certificate that lacks an expected Security Identifier (SID) extension. In deployments configured with SID-based certificate mapping rules, the service fails to verify the presence of the extension before processing it, causing the process to crash during authentication or lookup operations.
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Analysis
by VulDB Data Team • 10/06/2026
The System Security Services Daemon, commonly known as SSSD, serves as a critical component in Linux and Unix environments for managing identity and access control. It acts as an intermediary between local services such as SSH, sudo, and PAM, and remote identity providers like Active Directory or LDAP servers. In configurations where organizations rely on certificate-based authentication mechanisms mapped to user identities via Security Identifiers (SIDs), the integrity of these mappings is paramount for secure operation. The vulnerability described herein represents a significant flaw in how SSSD handles X.509 certificates during this mapping process, specifically when dealing with malformed or incomplete certificate structures that omit expected extensions.
The technical root cause of this denial-of-service condition lies in a lack of defensive programming practices regarding input validation within the certificate parsing logic. When an administrator configures SID-based certificate mapping rules, SSSD expects incoming client certificates to contain specific X.509 extensions, particularly those carrying the Security Identifier data required for user lookup and authentication. However, the software fails to perform a preliminary check to verify that this expected extension is present before attempting to parse or process its contents. Instead of gracefully handling the absence of the extension by returning an appropriate error code indicating invalid credentials, the daemon proceeds with operations on null or uninitialized memory pointers associated with the missing data structure. This logical oversight leads directly to a segmentation fault or similar critical failure within the SSSD worker processes responsible for authentication and identity lookups.
From an operational perspective, this vulnerability allows any remote attacker who can establish a TLS connection to the SSSD service to trigger a crash simply by presenting a certificate that lacks the required SID extension. This does not require complex exploitation techniques or prior knowledge of internal system states; it relies solely on the submission of a specifically crafted but structurally simple malformed certificate. The impact is immediate and severe, resulting in the termination of affected SSSD processes. In many deployments, this leads to a broader denial-of-service condition where legitimate users are unable to authenticate, SSH sessions cannot be established, or sudo privileges cannot be verified until the service is manually restarted by an administrator. This disruption can halt business operations significantly if high availability measures such as automatic restarts with health checks are not properly configured or if multiple nodes in a cluster fail simultaneously due to coordinated attacks.
This flaw aligns closely with CWE-20, which describes Improper Input Validation, specifically the failure to validate that required data elements exist before processing them. It also relates to CWE-476, NULL Pointer Dereference, as the crash is typically caused by attempting to access memory locations associated with non-existent certificate extensions. In terms of offensive security frameworks, this vulnerability can be leveraged within MITRE ATT&CK technique T1498, Network Denial of Service, where an attacker disrupts service availability through resource exhaustion or application crashes rather than overwhelming network bandwidth. The attack vector is classified as remote and requires no authentication to execute the initial trigger, although it only results in a crash rather than code execution, limiting its direct impact on confidentiality and integrity while severely impacting availability.
Mitigation strategies for this vulnerability primarily involve applying vendor-provided patches that update SSSD to versions where input validation has been strengthened. Administrators should ensure their systems are updated with the latest security errata released by their respective Linux distributions or upstream maintainers. In environments where immediate patching is not feasible, network-level controls can provide temporary relief. Implementing strict firewall rules or access control lists that restrict TLS connections to SSSD ports solely from trusted IP ranges reduces the attack surface available to remote attackers. Additionally, deploying a reverse proxy or load balancer in front of SSSD instances with certificate validation capabilities can filter out malformed requests before they reach the vulnerable service logic. Organizations should also review their certificate management policies to ensure that all issued certificates intended for SID mapping include the necessary extensions, thereby reducing the likelihood of encountering such anomalies even if unpatched systems remain in use temporarily. Regular auditing of authentication logs for repeated failed attempts or process restarts can help detect potential exploitation activities early.