CVE-2026-98777 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
binder: fix leaked fd fixups on TF_UPDATE_TXN supersede
When a TF_UPDATE_TXN transaction supersedes a pending async transaction in a frozen process, the outdated transaction is freed with kfree() directly. This skips binder_free_txn_fixups(), leaking all binder_txn_fd_fixup entries and their fget()'d struct file references.
The leaked file refcounts never reach zero, so the struct file objects are permanently pinned in memory. They survive process exit and accumulate across invocations until file-max exhaustion.
Every other transaction cleanup path (binder_free_transaction(), binder_transaction() error paths, binder_release_work()) correctly calls binder_free_txn_fixups(). Add the missing call before kfree() in the t_outdated cleanup block.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel's Binder IPC mechanism contains a resource management flaw within its transaction handling logic that leads to file descriptor leaks and subsequent memory exhaustion. This vulnerability specifically manifests when a TF_UPDATE_TXN transaction supersedes a pending asynchronous transaction belonging to a frozen process. In this specific operational scenario, the outdated or superseded transaction is deallocated using kfree() directly without invoking the necessary cleanup routine binder_free_txn_fixups(). This omission bypasses critical housekeeping steps required for proper resource reclamation within the Binder subsystem.
The technical consequence of skipping binder_free_txn_fixups() is a significant leak of internal data structures and kernel object references. Specifically, all entries in the binder_txn_fd_fixup list are leaked along with their associated struct file references obtained via fget(). Because these file reference counts never reach zero due to the missing release call, the underlying struct file objects remain permanently pinned in memory. This behavior prevents the kernel from reclaiming these resources even after the affected process has terminated or exited, leading to a persistent accumulation of leaked memory across multiple invocations and system uptime periods.
From an operational impact perspective, this vulnerability can lead to severe resource exhaustion on the host system. As the number of such superseded transactions increases over time, particularly in environments with high Binder IPC activity involving frozen processes, the unbounded growth of pinned struct file objects consumes kernel memory resources. Eventually, this accumulation drives the system toward file-max exhaustion, a state where no new files or sockets can be opened by any process on the system. This effectively results in a denial of service condition for all applications relying on Binder IPC and general file descriptor allocation, potentially causing widespread application failures and system instability without requiring external network access or complex exploitation techniques beyond normal usage patterns that trigger this specific transaction flow.
The root cause is identified as an inconsistency in error handling and cleanup paths within the Binder driver codebase. While other transaction cleanup mechanisms such as binder_free_transaction(), various error paths within binder_transaction(), and binder_release_work() correctly invoke binder_free_txn_fixups() to ensure proper resource release, the t_outdated cleanup block responsible for handling superseded transactions was missing this critical call. The resolution involves adding the missing invocation of binder_free_txn_fixups() immediately before the kfree() operation in the relevant code path. This ensures that all associated file descriptor fixups and their reference counts are properly decremented and cleaned up, preventing the accumulation of pinned kernel objects.
This vulnerability aligns with CWE-401, which describes a missing release of memory after effective usage, leading to resource leaks. Furthermore, from an adversarial perspective, this flaw can be leveraged for denial-of-service attacks against Linux-based systems utilizing Binder IPC, such as Android devices or embedded systems relying on similar inter-process communication mechanisms. The ATT&CK framework categorizes such behavior under Resource Hijacking techniques where attackers consume system resources to degrade availability. Mitigation strategies primarily involve applying the kernel patch that corrects the cleanup logic in the binder driver. System administrators should ensure their kernels are updated with this fix and monitor file descriptor usage metrics for anomalies indicative of rapid, unexplained growth in open files associated with Binder transactions.