high CVSS 7.8

CVE-2024-56740·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: nfs/localio: must clear res.replen in nfs_local_read_done Otherwise memory corruption can occur due to NFSv3 LOCALIO reads leaving garbage in res.replen: - nfs3_read_done() copies that into server->read_hdrsize; from there nfs3_proc_read_setup() copies it to args.replen in new requests. - nfs3_xdr_enc_read3args() passes that to rpc_prepare_reply_pages() which includes it in hdrsize for xdr_init_pages, so that rq_rcv_buf contains a ridiculous len. - This is copied to rq_private_buf and xs_read_stream_request() eventually passes the kvec to sock_recvmsg() which receives incoming data into entirely the wrong place. This is easily reproduced with NFSv3 LOCALIO that is servicing reads when it is made to pivot back to using normal RPC. This switch back to using normal NFSv3 with RPC can occur for a few reasons but this issue was exposed with a test that stops and then restarts the NFSv3 server while LOCALIO is performing heavy read IO.

Severity
high
Software
Kernel
Fixed in
6.12.2
Published
2024-12-29

Affected versions

From: 6.12

Until: 6.12.2

Fixed in: 6.12.2

How to fix this CVE

Update your Linux kernel to version 6.12.2 or later to resolve a critical memory corruption issue in NFSv3 LOCALIO read operations. This vulnerability occurs when the kernel fails to properly clear internal state during local NFS reads, causing garbage data to be interpreted as buffer sizes in subsequent network operations. Systems using NFSv3 with LOCALIO functionality that may fall back to standard RPC should prioritize this update immediately.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Check your kernel version with: uname -r — compare against 6.12.0 to 6.12.2 to identify vulnerable versions
  2. Verify NFSv3 LOCALIO is enabled by checking: grep -i localio /boot/config-$(uname -r) and confirming CONFIG_NFS_LOCALIO=y
  3. Review kernel logs for memory corruption indicators: dmesg | grep -i 'memory corruption\|buffer overflow\|invalid address' or sudo journalctl -u kernel -n 500 | grep -E 'Oops|BUG|segfault'
  4. After patching, confirm the updated kernel is loaded with: uname -r and verify it shows version 6.12.2 or later

FAQ

What is CVE-2024-56740?

CVE-2024-56740 is a kernel memory corruption vulnerability in NFSv3 LOCALIO (local I/O optimization) where uninitialized read response metadata causes subsequent network operations to interpret garbage data as buffer boundaries, leading to out-of-bounds memory writes.

Is CVE-2024-56740 being actively exploited?

No — CISA has not listed CVE-2024-56740 in the Known Exploited Vulnerabilities (KEV) catalog, and no public exploits are currently available. However, the memory corruption impact warrants rapid patching.

What versions of Kernel are affected by CVE-2024-56740?

Linux kernel versions 6.12.0, 6.12.1, and 6.12.2 are affected. The vulnerability was resolved in kernel 6.12.2 and later stable releases.

How do I check if my server is vulnerable to CVE-2024-56740?

Run uname -r to display your kernel version; if it reports 6.12.0 or 6.12.1, your system is vulnerable. Additionally, verify NFSv3 LOCALIO support with grep CONFIG_NFS_LOCALIO /boot/config-$(uname -r).

Does Defensia detect CVE-2024-56740?

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-2024-56740 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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