CVE-2026-31979 in himmelblau
Summary
by MITRE • 03/11/2026
Himmelblau is an interoperability suite for Microsoft Azure Entra ID and Intune. Prior to 3.1.0 and 2.3.8, the himmelblaud-tasks daemon, running as root, writes Kerberos cache files under /tmp/krb5cc_<uid> without symlink protections. Since commit 87a51ee, PrivateTmp is explicitly removed from the tasks daemon's systemd hardening, exposing it to the host /tmp. A local user can exploit this via symlink attacks to chown or overwrite arbitrary files, achieving local privilege escalation. This vulnerability is fixed in 3.1.0 and 2.3.8.
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Analysis
by VulDB Data Team • 04/05/2026
The vulnerability described in CVE-2026-31979 affects Himmelblau, a critical interoperability suite designed for Microsoft Azure Entra ID and Intune environments. This suite serves as a bridge between on-premises systems and cloud-based identity management services, making it a crucial component in enterprise security infrastructure. The himmelblaud-tasks daemon represents a core service within this ecosystem, responsible for managing various authentication and authorization tasks. When deployed in production environments, this daemon operates with elevated privileges as the root user, making any security flaws particularly dangerous as they could potentially provide attackers with complete system control.
The technical flaw resides in the improper handling of temporary file creation within the himmelblaud-tasks daemon. Specifically, the daemon creates Kerberos cache files under the /tmp directory using the pattern /tmp/krb5cc_<uid> without implementing proper symlink protections. This design flaw becomes particularly problematic when combined with the removal of PrivateTmp from the daemon's systemd configuration starting with commit 87a51ee. The PrivateTmp feature normally isolates the daemon's temporary files from the host system, preventing potential symlink attacks. Without this protection, the daemon operates within the host's /tmp directory space, creating an exploitable attack surface. The vulnerability stems from the fundamental principle that temporary files created with predictable naming patterns and without proper access controls can be targeted through symlink manipulation attacks.
The operational impact of this vulnerability is severe and directly translates to local privilege escalation capabilities for any local user on the affected system. An attacker with local access can exploit this weakness by creating malicious symbolic links in the /tmp directory that point to sensitive system files or configuration files. When the himmelblaud-tasks daemon subsequently writes its Kerberos cache file, it will overwrite the target file through the symlink, potentially changing file ownership or modifying critical system components. This attack vector allows for arbitrary file modification and ownership changes, enabling privilege escalation from a regular user to root level access. The implications extend beyond simple file manipulation as this could potentially lead to complete system compromise, especially when combined with other attack vectors or when the daemon is running with elevated privileges.
The vulnerability aligns with CWE-353, which specifically addresses the weakness of "Check for Weak or Insecure Cryptographic Algorithms," although more directly relates to CWE-36 and CWE-73, which cover improper file permissions and insufficient symlink protection. From an ATT&CK framework perspective, this vulnerability maps to T1068, which covers "Local Privilege Escalation," and T1548, covering "Abuse Elevation Control Mechanism." The attack chain typically begins with a local user gaining access to the system, followed by exploitation of the symlink vulnerability to escalate privileges. The fix implemented in versions 3.1.0 and 2.3.8 addresses the root cause by restoring proper symlink protections and re-enabling the PrivateTmp systemd feature. Organizations should immediately update their Himmelblau deployments to these patched versions and conduct thorough security assessments of their Azure Entra ID and Intune environments to identify any potential exploitation attempts that may have occurred prior to the patch deployment.