CVE-2026-107886 in CUPS
Summary
by MITRE • 10/09/2026
OpenPrinting CUPS before 2.4.20 contains a double-free in printer-class management. When CUPS-Add-Modify-Class replaces an existing class member list, add_class() frees pclass->printers without clearing the pointer. If subsequent validation fails, the class retains the dangling pointer; CUPS-Delete-Class subsequently frees the same allocation in cupsdDeletePrinter(). A client authorized to modify and delete classes can cause scheduler-wide denial of service. The default policy requires @SYSTEM privileges.
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Analysis
by VulDB Data Team • 10/09/2026
The vulnerability identified within OpenPrinting CUPS versions prior to 2.4.20 represents a critical memory management flaw located specifically in the printer-class management subsystem. This issue manifests as a double-free error, a category of software defect classified under CWE-415 in the Common Weakness Enumeration standard. The root cause lies in the add_class function, which is invoked when CUPS-Add-Modify-Class attempts to replace an existing class member list. During this operation, the application frees the memory allocation associated with pclass->printers but fails to nullify or clear the pointer immediately after deallocation. This oversight leaves a dangling pointer that still references the now-invalidated memory region within the internal data structures of the CUPS scheduler daemon.
The operational impact of this flaw is triggered when subsequent validation checks fail for the new class configuration. Because the pointer was not cleared, the application retains reference to the freed memory block rather than an empty or null state. When a client subsequently issues a request to delete the class using CUPS-Delete-Class, the cupsdDeletePrinter function attempts to free the same allocation again. This second attempt to release already-freed memory results in undefined behavior, typically leading to heap corruption and immediate termination of the scheduler process. Consequently, this vulnerability enables an authenticated attacker to cause a denial of service against the entire print scheduling infrastructure by repeatedly triggering the add and delete cycles that exploit the double-free condition.
From a threat modeling perspective aligned with MITRE ATT&CK techniques, this vulnerability facilitates Denial of Service (T1499) through resource exhaustion or application crash mechanisms. The attack vector requires local access to the CUPS service API, meaning an attacker must have valid credentials and sufficient privileges to modify printer classes. Under default security policies, these actions require @SYSTEM privileges, which restricts exploitation to users with high-level administrative rights on the host system. While this limits the scope of potential attackers compared to remote unauthenticated exploits, it remains a significant risk for environments where privilege escalation or insider threats are concerns, as compromising an account with class modification rights allows for immediate disruption of print services.
Mitigation strategies primarily involve upgrading the CUPS installation to version 2.4.20 or later, where this memory management logic has been corrected by ensuring pointers are properly nullified after deallocation. In environments where immediate patching is not feasible, administrators should enforce strict access controls on the @SYSTEM group and audit logs for frequent class modification attempts that could indicate exploitation activity. Additionally, enabling core dump analysis can assist in identifying instances of heap corruption resulting from this flaw during forensic investigations following a service outage.