medium CVSS 5.5

CVE-2024-40921·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: net: bridge: mst: pass vlan group directly to br_mst_vlan_set_state Pass the already obtained vlan group pointer to br_mst_vlan_set_state() instead of dereferencing it again. Each caller has already correctly dereferenced it for their context. This change is required for the following suspicious RCU dereference fix. No functional changes intended.

Severity
medium
Software
Kernel
Fixed in
6.9.6
Published
2024-07-12

Affected versions

From: 6.9.3

Until: 6.9.6

Fixed in: 6.9.6

How to fix this CVE

Update your Linux kernel to version 6.9.6 or later to resolve a memory dereferencing issue in the bridge MST (Multiple Spanning Tree) VLAN state management code. This patch improves code safety by eliminating redundant pointer dereferencing operations that could lead to inconsistent behavior. Systems running kernel versions 6.9.3 through 6.9.5 should prioritize this update.

sudo dnf update kernel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check your installed kernel version with: uname -r
  2. Step 2: Verify if your system is affected by comparing against 6.9.3-6.9.5 range: if [[ $(uname -r) =~ 6\.9\.[3-5] ]]; then echo 'Vulnerable'; fi
  3. Step 3: Review kernel logs for MST VLAN state changes: dmesg | grep -i 'mst\|vlan\|bridge'
  4. Step 4: Confirm the patch was applied by verifying kernel version is 6.9.6 or later: uname -r | grep -E '6\.9\.[6-9]|6\.(1[0-9]|[2-9][0-9])'
  5. Step 5: Check if bridge module is loaded: lsmod | grep bridge

FAQ

What is CVE-2024-40921?

CVE-2024-40921 is a kernel vulnerability in Linux bridge MST (Multiple Spanning Tree) code where VLAN group pointers were being dereferenced redundantly, potentially causing memory safety issues in bridge network configurations.

Is CVE-2024-40921 being actively exploited?

No, CVE-2024-40921 is not being actively exploited in the wild, and no public exploits are currently available. However, it should still be patched as part of regular security updates.

What versions of Kernel are affected by CVE-2024-40921?

Linux kernel versions 6.9.3 through 6.9.5 are affected. The vulnerability is resolved in kernel 6.9.6 and later versions.

How do I check if my server is vulnerable to CVE-2024-40921?

Run `uname -r` to display your kernel version. If it shows 6.9.3, 6.9.4, or 6.9.5, your system is vulnerable and requires immediate kernel update.

Does Defensia detect CVE-2024-40921?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2024-40921 will appear in your dashboard with remediation steps.

Related Kernel CVEs

CVE-2026-100075CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: RDMA/srpt: Fix srpt_alloc_rw_ctxs() unwind counters When srpt_alloc_rw_ctxs() fails partway through a multi-buffer indirect descriptor, the unwind path destroys RDMA contexts but leaves stale n_rw_ctx and n_rdma values (and a dangling rw_ctxs pointer). Later sq_wr_avail accounting in srpt_queue_response() or srpt_write_pending() can then subtract the wrong number of send queue credits. Reset the counters and clear rw_ctxs after freeing the heap allocation before returning an error.
CVE-2026-64439CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: crypto: krb5 - filter out async aead implementations at alloc krb5_aead_encrypt(), krb5_aead_decrypt() in rfc3961_simplified.c and rfc8009_encrypt(), rfc8009_decrypt() in rfc8009_aes2.c set a NULL completion callback and treat any negative return from crypto_aead_{encrypt,decrypt}() as terminal, falling through to kfree_sensitive(buffer). When the encrypt_name resolves to an async AEAD instance the request returns -EINPROGRESS, the buffer is freed while the backend's worker still holds a pointer, and the worker dereferences the freed slab on completion. KASAN report under UML+SLUB with a synthetic async aead backend bound to krb5->encrypt_name: BUG: KASAN: slab-use-after-free in t5_stub_complete+0x7d/0xc7 The helpers were written synchronously, so filter the async instances out at allocation time instead of plumbing crypto_wait_req() through every call site. Reachable via net/rxrpc/rxgk.c, fs/afs/cm_security.c and net/ceph/crypto.c on systems with an async AEAD provider bound to the krb5 enctype name.
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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