high CVSS 7.8

CVE-2025-21734·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: misc: fastrpc: Fix copy buffer page size For non-registered buffer, fastrpc driver copies the buffer and pass it to the remote subsystem. There is a problem with current implementation of page size calculation which is not considering the offset in the calculation. This might lead to passing of improper and out-of-bounds page size which could result in memory issue. Calculate page start and page end using the offset adjusted address instead of absolute address.

Severity
high
Software
Kernel
Fixed in
6.13.3
Published
2025-02-27

Affected versions

From: 6.13

Until: 6.13.3

Fixed in: 6.13.3

How to fix this CVE

Update your Linux kernel to version 6.13.3 or later to resolve a memory calculation vulnerability in the fastrpc driver that affects non-registered buffer handling. This patch corrects improper page size calculations when processing buffers, preventing potential memory access violations and system instability. Systems running kernel versions 6.13 through 6.13.2 should prioritize this update.

sudo dnf update kernel kernel-devel kernel-headers

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed kernel version: uname -r — ensure it is not in the 6.13.0-6.13.2 range
  2. Verify fastrpc module is loaded: lsmod | grep fastrpc — if not present, vulnerability exposure is minimal but update is still recommended
  3. Review kernel compilation options: grep CONFIG_FASTRPC /boot/config-$(uname -r) — look for =y or =m to determine if fastrpc is enabled
  4. After patching, reboot and confirm new kernel version: uname -r — should show 6.13.3 or later

FAQ

What is CVE-2025-21734?

This vulnerability affects the Linux kernel's fastrpc driver buffer handling. When copying unregistered buffers to remote subsystems, the driver miscalculates memory page boundaries by ignoring buffer offsets, potentially causing out-of-bounds memory access and system instability.

Is CVE-2025-21734 being actively exploited?

No, this vulnerability is not listed on CISA's Known Exploited Vulnerabilities (KEV) catalog and no public exploits are currently available. However, the high CVSS score (7.8) warrants prompt patching.

What versions of Kernel are affected by CVE-2025-21734?

Linux kernel versions 6.13 through 6.13.2 are affected. Kernel 6.13.3 and later include the fix.

How do I check if my server is vulnerable to CVE-2025-21734?

Run 'uname -r' and verify the output. If it shows 6.13.0, 6.13.1, or 6.13.2, your system is vulnerable. Also confirm fastrpc is enabled with: grep CONFIG_FASTRPC /boot/config-$(uname -r)

Does Defensia detect CVE-2025-21734?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2025-21734 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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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-2026-64067CVSS 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).
CVE-2026-64068CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: netfs: Fix missing locking around retry adding new subreqs Fix netfs_retry_read_subrequests() and netfs_retry_write_stream() to take the appropriate lock when adding extra subrequests into stream->subrequests.
CVE-2026-64355CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: bpf: Reject fragmented frames in devmap Devmap broadcast redirects clone the packet for all but the last destination. For native XDP, that clone path copies only the linear xdp_frame data, while fragmented frames keep skb_shared_info in tailroom outside the linear area. Cloning such a frame leaves XDP_FLAGS_HAS_FRAGS set but without valid frag metadata, and the later free path can interpret uninitialized tail data as skb_shared_info, leading to an out-of-bounds access during frame return. Reject fragmented native XDP frames in dev_map_enqueue_clone(). Add the same restriction to the generic XDP clone path in dev_map_redirect_clone(). Generic XDP represents fragmented packets as nonlinear skbs, and rejecting them here keeps clone-based broadcast support aligned between native and generic XDP.

References

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