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CVE-2025-39866 is a use-after-free vulnerability in the Linux kernel writeback subsystem, specifically in __mark_inode_dirty(). The flaw is caused by a race condition during bdi_writeback switching for an inode. In the vulnerable sequence, __mark_inode_dirty() obtains and later uses inode->i_wb while another worker concurrently switches the inode to a new writeback structure and releases the old one. As a result, wb_wakeup_delayed() can access a bdi_writeback object that has already been freed. The issue was observed along a normal file-write path involving generic_update_time(), file_modified(), and filesystem write handlers such as ext4 buffered writes. The upstream fix resolves the race by holding the inode spinlock until wb_wakeup_delayed() has completed, preventing the stale writeback structure from being freed while still in use.
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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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