high CVSS 7

CVE-2021-47088·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: mm/damon/dbgfs: protect targets destructions with kdamond_lock DAMON debugfs interface iterates current monitoring targets in 'dbgfs_target_ids_read()' while holding the corresponding 'kdamond_lock'. However, it also destructs the monitoring targets in 'dbgfs_before_terminate()' without holding the lock. This can result in a use_after_free bug. This commit avoids the race by protecting the destruction with the corresponding 'kdamond_lock'.

Severity
high
Software
Kernel
Fixed in
5.15.12
Published
2024-03-04

Affected versions

From: 5.15

Until: 5.15.12

Fixed in: 5.15.12

How to fix this CVE

Update your Linux kernel to version 5.15.12 or later to resolve a race condition in the DAMON debugfs interface that could allow local attackers to trigger use-after-free memory corruption. Systems running kernel versions 5.15 through 5.15.11 should prioritize this update, as the vulnerability affects the monitoring target destruction mechanism when accessed concurrently with the debugfs interface.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check your current kernel version with 'uname -r' and compare against the affected range (5.15.0 to 5.15.11)
  2. Step 2: Verify if DAMON debugfs interface is enabled by checking 'grep -i damon /boot/config-$(uname -r)' for CONFIG_DAMON_DBGFS=y
  3. Step 3: Search kernel logs for use-after-free errors with 'sudo dmesg | grep -i "use-after-free\|use_after_free\|UAF"' or 'sudo journalctl -k | grep -i UAF'
  4. Step 4: After patching, run 'uname -r' to confirm you're running 5.15.12 or later, then verify no UAF messages appear during normal operation over 24-48 hours

FAQ

What is CVE-2021-47088?

This vulnerability is a race condition in the Linux kernel's DAMON (Data Access Monitoring) debugfs module where concurrent access to monitoring targets can trigger a use-after-free memory bug, potentially allowing local privilege escalation.

Is CVE-2021-47088 being actively exploited?

No, this vulnerability is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available, though local attackers with system access could craft an exploit.

What versions of Kernel are affected by CVE-2021-47088?

Linux kernel versions 5.15.0 through 5.15.11 are vulnerable. The fix was integrated in kernel 5.15.12 and later versions.

How do I check if my server is vulnerable to CVE-2021-47088?

Run 'uname -r' to get your kernel version. If it shows 5.15.x where x is 11 or lower, your system is vulnerable. Additionally check 'cat /boot/config-$(uname -r) | grep DAMON_DBGFS' to confirm DAMON debugfs is compiled in.

Does Defensia detect CVE-2021-47088?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2021-47088 will appear in your dashboard with remediation steps and patch availability status.

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CVE-2026-64066CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: netfs: Fix netfs_read_to_pagecache() to pause on subreq failure Fix netfs_read_to_pagecache() so that it pauses the generation of new subrequests if an already-issued subrequest fails.
CVE-2026-64383CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: smb: client: fix double-free in SMB2_flush() replay SMB2_flush() keeps its response buffer bookkeeping across replay attempts. If a replayable flush response is received and the retry then fails before cifs_send_recv() stores a replacement response, flush_exit will free the stale response pointer a second time. Reinitialize resp_buftype and rsp_iov at the top of the replay loop so cleanup only acts on response state produced by the current attempt. This fixes a double-free without changing replay handling for successful requests.
CVE-2026-64067CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: netfs: Fix missing barriers when accessing stream->subrequests locklessly The list of subrequests attached to stream->subrequests is accessed without locks by netfs_collect_read_results() and netfs_collect_write_results(), and then they access subreq->flags without taking a barrier after getting the subreq pointer from the list. Relatedly, the functions that build the list don't use any sort of write barrier when constructing the list to make sure that the NETFS_SREQ_IN_PROGRESS flag is perceived to be set first if no lock is taken. Fix this by: (1) Add a new list_add_tail_release() function that uses a release barrier to set the pointer to the new member of the list. (2) Add a new list_first_entry_or_null_acquire() function that uses an acquire barrier to read the pointer to the first member in a list (or return NULL). (3) Use list_add_tail_release() when adding a subreq to ->subrequests. (4) Use list_first_entry_or_null_acquire() when initially accessing the front of the list (when an item is removed, the pointer to the new front iterm is obtained under the same lock).

References

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