critical CVSS 9.8

CVE-2026-43185·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix signededness bug in smb_direct_prepare_negotiation() smb_direct_prepare_negotiation() casts an unsigned __u32 value from sp->max_recv_size and req->preferred_send_size to a signed int before computing min_t(int, ...). A maliciously provided preferred_send_size of 0x80000000 will return as smaller than max_recv_size, and then be used to set the maximum allowed alowed receive size for the next message. By sending a second message with a large value (>1420 bytes) the attacker can then achieve a heap buffer overflow. This fix replaces min_t(int, ...) with min_t(u32)

Severity
critical
Software
Kernel
Fixed in
6.19.6
Published

Affected versions

From: 6.19

Until: 6.19.6

Fixed in: 6.19.6

How to fix this CVE

Update your Linux kernel to version 6.19.6 or later to patch a critical signededness bug in the SMB Direct protocol handler. This vulnerability allows remote attackers to trigger heap buffer overflows through crafted SMB negotiation messages. Immediately apply kernel updates and reboot your systems to eliminate exposure to this network-reachable flaw.

sudo dnf update kernel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed kernel version: uname -r | grep -E '^6\.19\.[0-5]' && echo 'VULNERABLE' || echo 'PATCHED or different kernel'
  2. Verify SMB Direct (port 445) is accessible: ss -tlnp | grep ':445' to confirm ksmbd service is running and exposed
  3. Search kernel logs for heap corruption warnings: journalctl -u kernel --since='24 hours ago' | grep -i 'heap\|buffer\|overflow\|ksmbd'
  4. Confirm kernel upgrade applied: uname -r should show 6.19.6 or higher; verify with apt-cache policy linux-image-generic or dnf info kernel

FAQ

What is CVE-2026-43185?

A critical integer signedness bug in the Linux kernel's SMB Direct protocol negotiation handler that allows attackers to cause heap buffer overflows by sending specially crafted SMB negotiation packets with malicious size parameters.

Is CVE-2026-43185 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available. However, given the critical CVSS score of 9.8 and network accessibility, proactive patching is essential.

What versions of Kernel are affected by CVE-2026-43185?

Linux kernel versions 6.19 through 6.19.5 are affected. The fix was released in kernel 6.19.6. If you are running kernel 6.19.0, 6.19.1, 6.19.2, 6.19.3, 6.19.4, or 6.19.5, your system is vulnerable.

How do I check if my server is vulnerable to CVE-2026-43185?

Run `uname -r` and check if the output matches 6.19.0 through 6.19.5. If it does, you are vulnerable. Also verify ksmbd is active with `systemctl status ksmbd` or `ps aux | grep ksmbd`.

Does Defensia detect CVE-2026-43185?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2026-43185 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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CVE-2026-53398CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: NFSD: Fix SECINFO_NO_NAME decode error cleanup nfsd4_decode_secinfo_no_name() currently initializes sin_exp after decoding sin_style. If the XDR stream is truncated, the decoder returns nfserr_bad_xdr before sin_exp is initialized. Since commit 3fdc54646234 ("NFSD: Reduce amount of struct nfsd4_compoundargs that needs clearing"), the inline iops array is not cleared between RPC calls. A failed SECINFO_NO_NAME decode can therefore leave sin_exp holding stale union contents from a previous operation. The error response path still invokes nfsd4_secinfo_no_name_release(), which calls exp_put() on a non-NULL sin_exp. Initialize sin_exp before the first failable decode step, matching nfsd4_decode_secinfo().
CVE-2026-64125CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: bcmgenet: keep RBUF EEE/PM disabled Setting RBUF_EEE_EN | RBUF_PM_EN in RBUF_ENERGY_CTRL breaks the RX path on GENET hardware once MAC EEE becomes active. RX traffic stops flowing while the link stays up and the usual descriptor/RX error counters remain quiet. In that state the MAC still accepts frames (rbuf_ovflow_cnt keeps climbing) but RBUF no longer forwards them to DMA, so rx_packets is no longer incremented at the netdev level. On some boards the corruption ends up as a paging fault in skb_release_data via bcmgenet_rx_poll on an LPI exit. Reproduced on Pi 4B (BCM2711 + BCM54213PE) and confirmed by Florian Fainelli on an internal Broadcom 4908-family board with the same crash signature. RBUF_PM_EN is not publicly documented. This shows up more often now that phy_support_eee() enables EEE by default, but it also affects older kernels as soon as TX LPI is turned on via ethtool, so it is not specific to recent changes. Always clear RBUF_EEE_EN | RBUF_PM_EN in bcmgenet_eee_enable_set so the bits stay off across resets. UMAC and TBUF setup is left alone so TX-side EEE keeps working.
CVE-2026-98548CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: sctp: discard the rest of the packet on a stale-cookie error When an association is in COOKIE-ECHOED state and the peer sends a bundled [ERROR(Stale Cookie)][DATA] packet from one of its non-primary addresses, processing the ERROR chunk takes the non-fatal stale-cookie retry path sctp_sf_do_5_2_6_stale(), which queues SCTP_CMD_DEL_NON_PRIMARY while keeping the association alive. sctp_cmd_del_non_primary() removes every non-primary transport - including the very transport this packet arrived on, which is still referenced by the receive lookup and shared by all chunks of the packet via chunk->transport. sctp_assoc_rm_peer() does redirect asoc->peer.last_data_from away from the removed transport, but right afterwards the bundled DATA chunk makes sctp_assoc_bh_rcv() re-register asoc->peer.last_data_from = chunk->transport unconditionally, undoing the redirection with the just-removed transport. Once the packet is done, the receive reference is dropped and the transport is RCU-freed, while the surviving association keeps the dangling last_data_from. A later FWD-TSN (or the delayed SACK timer) makes sctp_gen_sack() dereference it (->param_flags and friends), and sctp_make_sack()/sctp_outq_select_transport() may write to the freed object and link it into the live transport list. This is a use-after-free triggerable by any malicious SCTP peer (or a local unprivileged user acting as one) with no capabilities required: BUG: KASAN: slab-use-after-free in sctp_do_sm+0x498a/0x5660 Read of size 4 at addr ffff88800e1e356c by task poc/115 Call Trace: sctp_do_sm <- sctp_assoc_bh_rcv <- sctp_inq_push <- sctp_rcv <- ip_protocol_deliver_rcu <- ip_rcv Allocated: sctp_transport_new <- sctp_assoc_add_peer <- sctp_process_init (INIT-ACK processing) Freed: kfree <- sctp_transport_destroy_rcu <- rcu_core (call_rcu queued by sctp_transport_put at end of sctp_rcv) The buggy address is located 364 bytes inside of freed 1024-byte region [ffff88800e1e3400, ffff88800e1e3800), cache kmalloc-1k Note that commit 03a9d10ecf71 ("sctp: drop a chunk if its transport was removed") only covers the window between the receive lookup and the chunk processing (e.g. an ASCONF DEL-IP racing the socket backlog); here the transport is removed *while* the packet is being processed, by an earlier chunk of the same packet, so the drop in sctp_inq_push() does not reach this path. Verified with the bundled [ERROR(Stale Cookie)][DATA] + FWD-TSN reproducer: the KASAN report above still fires with that commit applied, and is gone with this patch on top. Fix it by discarding the rest of the packet on this path, as suggested by Xin. After the stale-cookie ERROR has sent the association back to COOKIE-WAIT and removed the non-primary transports, the remaining chunks of the packet can only run against the restarted handshake while referencing the removed arrival transport through chunk->transport: besides the last_data_from registration above, sctp_cmd_setup_t2() and the sctp_make_*() reply builders would also copy that pointer into association-lifetime state that sctp_assoc_rm_peer() has already sanitized. Let the peer retransmit them, in line with what sctp_inq_push() does for chunks whose transport was removed before processing.
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References

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