critical CVSS 9.8

CVE-2026-64385·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix double-free in SMB2_ioctl() replay A response-bearing attempt can return a replayable error and free its response buffer. If SMB2_ioctl_init() fails before the next send, cleanup retains the previous buffer type and frees that response again. Reset response bookkeeping before each attempt to prevent the stale free.

Severity
critical
Software
Kernel
Fixed in
7.1.4
Published
2026-07-25

Affected versions

From: 6.19

Until: 7.1.4

Fixed in: 7.1.4

How to fix this CVE

Update your Linux kernel to version 7.1.4 or later to patch a critical double-free vulnerability in SMB2 ioctl operations that could allow local privilege escalation or denial of service. The vulnerability occurs when SMB2_ioctl() replay logic fails to properly reset response buffer bookkeeping, causing a previously-freed buffer to be freed again during error handling. Prioritize this update as it affects kernel versions 6.19 through 7.1.3 with a CVSS score of 9.8.

sudo dnf update kernel kernel-headers 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 (6.19 to 7.1.3)
  2. Step 2: Verify SMB client functionality is enabled in your kernel config with `grep CONFIG_CIFS /boot/config-$(uname -r)` (should show CONFIG_CIFS=y or =m)
  3. Step 3: Search system logs for SMB2 ioctl errors using `journalctl -u kernel | grep -i 'smb2\|ioctl\|replay' | head -20`
  4. Step 4: After patching, confirm kernel version with `uname -r` shows 7.1.4 or later and reboot to activate changes

FAQ

What is CVE-2026-64385?

This is a double-free memory corruption vulnerability in the Linux kernel's SMB2 client implementation. When an SMB2 ioctl operation encounters a replayable error during retry logic, the response buffer cleanup fails to reset its bookkeeping state, leading to the same buffer being freed twice and potentially allowing code execution with kernel privileges.

Is CVE-2026-64385 being actively exploited?

No, this vulnerability is not currently listed on CISA's Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available. However, the CVSS 9.8 severity warrants immediate patching due to the critical nature of the flaw.

What versions of Kernel are affected by CVE-2026-64385?

Linux kernel versions 6.19 through 7.1.3 are vulnerable. Kernel 7.1.4 and later versions contain the fix.

How do I check if my server is vulnerable to CVE-2026-64385?

Run `uname -r` to get your kernel version. If it shows 6.19.x through 7.1.3, you are vulnerable. Cross-reference with `grep CONFIG_CIFS /boot/config-$(uname -r)` to confirm SMB2 client support is compiled in.

Does Defensia detect CVE-2026-64385?

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-2026-64385 will appear in your dashboard with remediation steps.

Related Kernel CVEs

CVE-2026-64033CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: RDMA/rtrs: Fix use-after-free in path file creation cleanup In the error path of rtrs_srv_create_path_files(), the sysfs root folders may already have been created and srv_path->kobj may already have been initialized. If a later step fails, the cleanup currently calls kobject_put(&srv_path->kobj) before rtrs_srv_destroy_once_sysfs_root_folders(srv_path). kobject_put() may drop the last reference to srv_path->kobj and invoke the release callback, rtrs_srv_release(), which frees srv_path. The following call to rtrs_srv_destroy_once_sysfs_root_folders(srv_path) then dereferences srv_path internally to access srv_path->srv, resulting in a use-after-free. This failure path is reached before rtrs_srv_create_path_files() returns success, so the successful-path lifetime handling is not involved. Fix this by destroying the sysfs root folders before calling kobject_put(&srv_path->kobj), so srv_path is still valid while the helper accesses it. This issue was found by a static analysis tool I am developing.
CVE-2026-64037CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: wifi: iwlwifi: mld: fix TSO segmentation explosion when AMSDU is disabled When the TLC notification disables AMSDU for a TID, the MLD driver sets max_tid_amsdu_len to the sentinel value 1. The TSO segmentation path in iwl_mld_tx_tso_segment() checks for zero but not for this sentinel, allowing it to reach the num_subframes calculation: num_subframes = (max_tid_amsdu_len + pad) / (subf_len + pad) = (1 + 2) / (1534 + 2) = 0 This zero propagates to iwl_tx_tso_segment() which sets: gso_size = num_subframes * mss = 0 Calling skb_gso_segment() with gso_size=0 creates over 32000 tiny segments from a single GSO skb. This floods the TX ring with ~1024 micro-frames (the rest are purged), creating a massive burst of TX completion events that can lead to memory corruption and a subsequent use-after-free in TCP's retransmit queue (refcount underflow in tcp_shifted_skb, NULL deref in tcp_rack_detect_loss). The MVM driver is immune because it checks mvmsta->amsdu_enabled before reaching the num_subframes calculation. The MLD driver has no equivalent bitmap check and relies solely on max_tid_amsdu_len, which does not catch the sentinel value. Fix this by detecting the sentinel value (max_tid_amsdu_len == 1) at the existing check and falling back to non-AMSDU TSO segmentation. Also add a WARN_ON_ONCE guard after the num_subframes division as defense-in-depth to catch any future code paths that produce zero through a different mechanism.
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-2026-63994CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]() Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head. Fix this possible UAF by initializing the local variables after the skb_cow() call. Remove skb_reset_network_header() calls which were not needed.
CVE-2026-64035CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: igc: set tx buffer type for SMD frames Sashiko pointed out that igc_fpe_init_smd_frame() initializes igc_tx_buffer fields for an SMD skb, but does not set the buffer type: https://sashiko.dev/#/patchset/20260415025226.114115-1-kohei%40enjuk.jp Since igc_tx_buffer entries are reused, a stale XDP or XSK type can remain and make TX completion use the wrong cleanup path. Set the buffer type to IGC_TX_BUFFER_TYPE_SKB.

References

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