CVE-2026-80877 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
afs: Fix vllist leak
Fix a leak of the new vllist in afs_update_cell() in the event that it is an empty list (nr_servers == 0), in which case the old list isn't displaced unless the old list is also empty.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified as AFS vlist leak represents a resource management flaw within the Linux kernel's Andrew File System implementation, specifically affecting the afs_update_cell function. This component of the kernel is responsible for maintaining and updating the cell database, which maps file server locations to specific cells in the distributed filesystem architecture. The core technical issue arises during the process of refreshing or replacing the list of available servers associated with a particular cell. When the system attempts to update this information by fetching new data from the network, it allocates memory for a new virtual list structure intended to hold the updated server addresses. Under normal operational conditions where the incoming data contains valid entries, this new list successfully replaces the existing one, and any previous resources are properly managed or discarded as part of the standard replacement protocol.
The critical flaw occurs when the newly fetched list is empty, indicated by a condition where the number of servers equals zero. In such scenarios, the code logic fails to correctly handle the memory allocation for this new empty structure. Specifically, if the existing old list also contains no entries, the system does not displace or free the previously allocated resources associated with the old state because it assumes that an empty-to-empty transition requires no structural change. However, the newly allocated vllist object remains in memory without being linked to any active data structure or subsequently freed by the garbage collection mechanisms of the kernel. This results in a direct memory leak where each occurrence of this specific update cycle with an empty server list consumes additional kernel heap space that is never reclaimed during the lifetime of the process or until system reboot if applicable, though typically such leaks accumulate over time as network conditions fluctuate.
From an operational impact perspective, while a single instance of this leak may seem negligible in terms of immediate memory consumption, its cumulative effect can be significant for systems operating continuously with dynamic cell configurations. Persistent memory leaks within the kernel space are particularly dangerous because they reduce the available pool of physical and virtual memory accessible to all processes running on the host. Over extended periods, especially in environments where AFS cells frequently update their server lists or experience intermittent connectivity issues leading to empty responses, this leak can contribute to gradual system degradation. In severe cases, continuous leakage could lead to out-of-memory conditions within kernel space, potentially causing process scheduling failures, increased latency for file operations, or even a complete system crash if the memory pressure becomes critical enough to trigger emergency reclamation mechanisms that fail to resolve the issue due to the nature of the leak being in non-swappable kernel allocations.
This vulnerability aligns with CWE-401, which describes a missing release of memory after effective usage, highlighting a failure in proper resource deallocation logic. The root cause is essentially an improper handling of edge cases in state transitions within data structure management routines. From a defensive perspective and mitigation strategy, the primary resolution involves patching the afs_update_cell function to ensure that any newly allocated list structures are either properly integrated into the active cell database or explicitly freed if they do not replace existing non-empty lists. System administrators should apply the latest kernel updates provided by their distribution vendors which include this specific fix. Additionally, monitoring tools such as kmemleak can be employed in development and staging environments to detect similar memory management anomalies before they impact production systems. Regular auditing of kernel logs for out-of-memory warnings or unusual memory usage patterns related to network filesystem drivers serves as a secondary layer of defense against the operational impacts of such resource exhaustion vulnerabilities.