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CVE-2025-39866 is a use-after-free vulnerability in the Linux kernel filesystem writeback subsystem. The __mark_inode_dirty() function can obtain a bdi_writeback object while a concurrent worker switches the inode to another writeback object. The switching path replaces inode->i_wb and releases the old object through wb_put_many() and cgwb_release(). If the inode lock has already been released, wb_wakeup_delayed() can subsequently access the freed object. The race was observed during an ext4 buffered write on an ARM64 kernel build based on Linux 6.6.56. Triggering the flaw can cause a kernel fault and potentially denial of service.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository contains a proof-of-concept (POC) exploit for CVE-2025-39866, a use-after-free (UAF) vulnerability in the Linux kernel (versions prior to 6.12.16) due to a missing spinlock in the writeback subsystem. The exploit is implemented as a Linux kernel module (poc.c) that, when loaded, creates two threads: one manipulates the writeback (wb) structure of a file inode, while the other schedules a work item that frees the same structure, creating a race condition. If successful, this results in a kernel panic or crash (denial of service). The exploit does not provide privilege escalation or a shell; it is strictly a POC for triggering the vulnerability. The only code file is 'poc.c', which contains the kernel module logic. The README.md provides detailed build and usage instructions, as well as background on the vulnerability and mitigation strategies. The exploit interacts with the '/tmp' directory and creates a file '/tmp/file.txt' as part of its operation. No network endpoints are involved; the attack vector is local, requiring the ability to load kernel modules.
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A race condition in Linux kernel filesystem writeback can cause a use-after-free in __mark_inode_dirty() when an inode's bdi_writeback structure is switched and the old structure is released before wb_wakeup_delayed() accesses it. The listed CVSS v3 base score is 7.8, with local access and low privileges required and potentially high confidentiality, integrity, and availability impacts. The fix holds the inode spinlock until wb_wakeup_delayed() finishes.
A Linux kernel writeback race condition causes a use-after-free in __mark_inode_dirty() when a bdi_writeback structure is switched and freed before wb_wakeup_delayed() accesses it. The fix holds the inode spinlock until wb_wakeup_delayed() finishes. The reference assigns a CVSS v3 base score of 7.8, indicating local exploitation requiring low privileges, with potentially high confidentiality, integrity, and availability impact.
Linux kernel filesystem writeback vulnerability involving a use-after-free in __mark_inode_dirty().
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