critical CVSS 9.8

CVE-2026-64383·Kernel vulnerability

In 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.

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 resolve a critical double-free memory corruption vulnerability in the SMB2 client flush operation. This flaw affects kernel versions 6.19 through 7.1.3 and can lead to kernel crashes or potential code execution during SMB protocol replay scenarios. Apply the patch immediately on all affected systems, particularly those using SMB/CIFS file sharing.

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 vulnerable range (6.19 to 7.1.3)
  2. Step 2: Verify SMB/CIFS client is enabled by checking `lsmod | grep cifs` or `grep -i cifs /proc/modules`
  3. Step 3: Review kernel logs for SMB flush errors or double-free warnings with `dmesg | grep -i 'double.*free\|smb.*flush\|cifs'` or check `/var/log/kern.log`
  4. Step 4: After patching, confirm the new kernel is loaded with `uname -r` and reboot if necessary with `sudo reboot`

FAQ

What is CVE-2026-64383?

CVE-2026-64383 is a critical double-free vulnerability in the Linux kernel's SMB2 client implementation that occurs when handling flush operations during protocol replay. If a flush response is received and a subsequent retry fails before the response buffer is properly replaced, the cleanup routine will attempt to free the same memory region twice, potentially causing a kernel panic or denial of service.

Is CVE-2026-64383 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities catalog and no public exploits are available. However, the critical CVSS 9.8 score indicates high severity and patches should be deployed promptly.

What versions of Kernel are affected by CVE-2026-64383?

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

How do I check if my server is vulnerable to CVE-2026-64383?

Run `uname -r` to obtain your kernel version and verify it falls within the 6.19 to 7.1.3 range. Additionally, confirm SMB/CIFS functionality is in use with `lsmod | grep cifs`. If both conditions are true, your system is vulnerable.

Does Defensia detect CVE-2026-64383?

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-2026-64383 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-2026-64397CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ksmbd: serialize QUERY_DIRECTORY requests per file smb2_query_dir() stores a pointer to its stack-allocated private data in the ksmbd_file readdir_data. Concurrent QUERY_DIRECTORY requests using the same file handle can overwrite this pointer while an iterate_dir() callback is still using it, resulting in a stack use-after-free. Add a per-file mutex and hold it while accessing the shared directory enumeration state. The lock covers scan restart, dot entry state, readdir_data setup and iteration, and response construction. This prevents another request from replacing readdir_data.private before the current request has finished using it and also serializes the shared file position.
CVE-2026-64399CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ksmbd: add permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE The FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() overwrites the destination file's data via vfs_clone_file_range() with neither the share-level KSMBD_TREE_CONN_FLAG_WRITABLE check nor a per-handle fp->daccess check that the other write-bearing arms carry. A client can overwrite destination data on a read-only share, or from a handle opened with only FILE_WRITE_ATTRIBUTES (which still yields an FMODE_WRITE filp). FILE_WRITE_ATTRIBUTES-only destination handle overwrote the file's data via the clone. Add both checks, matching the FSCTL_SET_SPARSE permission fix; require FILE_WRITE_DATA since this writes data.
CVE-2026-64046CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: tls: prevent chain-after-chain in plain text SG Sashiko points out that if end = 0 (start != 0) the current code will create a chain link to content type right after the wrap link: This would create a chain where the wrap link points directly to another chain link. The scatterlist API sg_next iterator does not recursively resolve consecutive chain links. meaning this is illegal input to crypto. The wrapping link is unnecessary if end = 0. end is the entry after the last one used so end = 0 means there's nothing pushed after the wrap: end start i v v v [ ]...[ ][ d ][ d ][ d ][ d ][rsv for wrap] Skip the wrapping in this case. TLS 1.3 can use the "wrapping slot" for it's chaining if end = 0. This avoids the chain-after-chain. Move the wrap chaining before marking END and chaining off content type, that feels like more logical ordering to me, but should not matter from functional perspective.
CVE-2026-52986CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_sip: don't use simple_strtoul Replace unsafe port parsing in epaddr_len(), ct_sip_parse_header_uri(), and ct_sip_parse_request() with a new sip_parse_port() helper that validates each digit against the buffer limit, eliminating the use of simple_strtoul() which assumes NUL-terminated strings. The previous code dereferenced pointers without bounds checks after sip_parse_addr() and relied on simple_strtoul() on non-NUL-terminated skb data. A port that reaches the buffer limit without a trailing character is also rejected as malformed. Also get rid of all simple_strtoul() usage in conntrack, prefer a stricter version instead. There are intentional changes: - Bail out if number is > UINT_MAX and indicate a failure, same for too long sequences. While we do accept 05535 as port 5535, we will not accept e.g. 'sip:10.0.0.1:005060'. While its syntactically valid under RFC 3261, we should restrict this to not waste cycles when presented with malformed packets with 64k '0' characters. - Force base 10 in ct_sip_parse_numerical_param(). This is used to fetch 'expire=' and 'rports='; both are expected to use base-10. - In nf_nat_sip.c, only accept the parsed value if its within the 1k-64k range. - epaddr_len now returns 0 if the port is invalid, as it already does for invalid ip addresses. This is intentional. nf_conntrack_sip performs lots of guesswork to find the right parts of the message to parse. Being stricter could break existing setups. Connection tracking helpers are designed to allow traffic to pass, not to block it. Based on an earlier patch from Jenny Guanni Qu <qguanni@gmail.com>.

References

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