CVE-2022-42320 in Xen
Summary
by MITRE • 11/01/2022
Xenstore: Guests can get access to Xenstore nodes of deleted domains Access rights of Xenstore nodes are per domid. When a domain is gone, there might be Xenstore nodes left with access rights containing the domid of the removed domain. This is normally no problem, as those access right entries will be corrected when such a node is written later. There is a small time window when a new domain is created, where the access rights of a past domain with the same domid as the new one will be regarded to be still valid, leading to the new domain being able to get access to a node which was meant to be accessible by the removed domain. For this to happen another domain needs to write the node before the newly created domain is being introduced to Xenstore by dom0.
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Analysis
by VulDB Data Team • 11/17/2024
The vulnerability described in CVE-2022-42320 represents a critical access control flaw within the Xen hypervisor's xenstore service that allows guest domains to potentially access sensitive information belonging to previously deleted domains. This issue stems from the fundamental design of xenstore's permission model where access rights are tied to domain identifiers or domid values. When a domain is terminated, the system should properly clean up all associated xenstore nodes and their corresponding access control entries. However, a temporal inconsistency exists in the cleanup process that creates a window of opportunity for privilege escalation attacks.
The technical flaw manifests through a race condition involving domain lifecycle management and xenstore node access control. Specifically, when a new domain is created with the same domid as a previously deleted domain, there exists a brief time interval during which the xenstore service maintains access rights entries referencing the old domain identifier. During this window, the newly created domain can exploit these stale permissions to access xenstore nodes that were originally intended to be restricted to the removed domain. This vulnerability directly violates the principle of least privilege and demonstrates a failure in proper resource cleanup and access control enforcement.
The operational impact of this vulnerability extends beyond simple information disclosure, potentially enabling malicious domains to access sensitive configuration data, guest state information, or other critical xenstore resources that should be isolated to specific domains. According to CWE-284, this represents an improper access control issue where the system fails to properly enforce access restrictions. The vulnerability creates a pathway for privilege escalation attacks where a guest domain could potentially gain unauthorized access to resources belonging to other domains, undermining the fundamental isolation guarantees that hypervisors must maintain. This weakness particularly affects environments where multiple domains operate simultaneously and where domain recreation with identical identifiers is common.
The attack scenario requires coordination between multiple domains, specifically needing another domain to write to a xenstore node before the newly created domain is properly introduced to the xenstore service by dom0. This dependency on external domain activity makes the vulnerability more subtle but still exploitable in multi-domain environments. From an ATT&CK perspective, this vulnerability aligns with techniques involving privilege escalation and credential access, as it allows an attacker to access resources that should be restricted to other domains. The temporal nature of the flaw makes it challenging to detect through standard monitoring approaches, as the vulnerability only exists during a very narrow window of time.
Mitigation strategies should focus on implementing proper access control cleanup mechanisms and eliminating the race condition that enables this vulnerability. System administrators should ensure that xenstore access control entries are properly invalidated immediately upon domain termination, rather than relying on deferred cleanup processes. Additionally, implementing stricter domain identifier allocation schemes that prevent reuse of domid values within reasonable timeframes can significantly reduce the attack surface. The fix should address the core issue by ensuring that xenstore access rights are properly cleared and that new domain creation does not inherit stale permissions from previously terminated domains. Organizations should also consider implementing monitoring solutions that can detect anomalous xenstore access patterns that might indicate exploitation attempts.