critical CVSS 9.8

CVE-2026-43198·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: tcp: fix potential race in tcp_v6_syn_recv_sock() Code in tcp_v6_syn_recv_sock() after the call to tcp_v4_syn_recv_sock() is done too late. After tcp_v4_syn_recv_sock(), the child socket is already visible from TCP ehash table and other cpus might use it. Since newinet->pinet6 is still pointing to the listener ipv6_pinfo bad things can happen as syzbot found. Move the problematic code in tcp_v6_mapped_child_init() and call this new helper from tcp_v4_syn_recv_sock() before the ehash insertion. This allows the removal of one tcp_sync_mss(), since tcp_v4_syn_recv_sock() will call it with the correct context.

Severity
critical
Software
Kernel
Fixed in
6.19.6
Published
2026-05-06

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 resolve a critical race condition in TCP IPv6 socket initialization that could allow remote attackers to trigger memory corruption. This patch reorganizes socket initialization code to prevent concurrent access to uninitialized IPv6 structures during connection establishment. Kernel updates typically require a system reboot to take effect.

sudo dnf check-update kernel && sudo dnf update kernel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check your kernel version: uname -r
  2. Verify if vulnerable version is installed: grep -i '6.19' /proc/version || echo 'Not vulnerable to this range'
  3. List loaded kernel modules related to TCP: lsmod | grep -E 'tcp|ipv6'
  4. After patching, confirm new kernel version: uname -r (should be 6.19.6 or later)
  5. Verify kernel update completed successfully: dmesg | tail -20 (should show new kernel boot messages)

FAQ

What is CVE-2026-43198?

CVE-2026-43198 is a critical race condition in the Linux kernel's TCP IPv6 implementation that occurs when a child socket becomes visible to other CPUs before its IPv6-specific fields are properly initialized, potentially leading to memory corruption and system crashes.

Is CVE-2026-43198 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are known to be available, though the critical CVSS score of 9.8 indicates high severity if exploited.

What versions of Kernel are affected by CVE-2026-43198?

Linux kernel versions 6.19 through 6.19.6 (inclusive) are affected; kernel 6.19.6 and all later versions contain the fix.

How do I check if my server is vulnerable to CVE-2026-43198?

Run 'uname -r' and compare your kernel version to the affected range (6.19 to 6.19.6); if your version falls within this range, your system is vulnerable and requires a kernel update.

Does Defensia detect CVE-2026-43198?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Linux kernel is installed on a monitored server running versions 6.19 through 6.19.6, CVE-2026-43198 will appear in your dashboard with remediation steps.

Related Kernel CVEs

CVE-2026-64303CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: spi: fsl-lpspi: terminate the RX channel on TX prepare failure path When dmaengine_prep_slave_sg() fails for the TX channel, the error path terminates the TX DMA channel but leaves the RX channel running. Since the RX channel was already submitted and issued prior to preparing the TX descriptor, returning -EINVAL causes the SPI core to unmap the DMA buffers while the RX DMA engine continues writing to them, leading to potential memory corruption or use-after-free. Terminate the RX channel before returning on the TX prepare failure path.
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.
CVE-2026-63993CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu() skb_tunnel_check_pmtu() can change skb->head. Reusing old_iph afer skb_tunnel_check_pmtu() can cause an UAF. Use instead ip_hdr(skb) as done in drivers/net/bareudp.c and drivers/net/geneve.c. Found by Sashiko.
CVE-2026-43501CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ipv6: rpl: reserve mac_len headroom when recompressed SRH grows ipv6_rpl_srh_rcv() decompresses an RFC 6554 Source Routing Header, swaps the next segment into ipv6_hdr->daddr, recompresses, then pulls the old header and pushes the new one plus the IPv6 header back. The recompressed header can be larger than the received one when the swap reduces the common-prefix length the segments share with daddr (CmprI=0, CmprE>0, seg[0][0] != daddr[0] gives the maximum +8 bytes). pskb_expand_head() was gated on segments_left == 0, so on earlier segments the push consumed unchecked headroom. Once skb_push() leaves fewer than skb->mac_len bytes in front of data, skb_mac_header_rebuild()'s call to: skb_set_mac_header(skb, -skb->mac_len); will store (data - head) - mac_len into the u16 mac_header field, which wraps to ~65530, and the following memmove() writes mac_len bytes ~64KiB past skb->head. A single AF_INET6/SOCK_RAW/IPV6_HDRINCL packet over lo with a two segment type-3 SRH (CmprI=0, CmprE=15) reaches headroom 8 after one pass; KASAN reports a 14-byte OOB write in ipv6_rthdr_rcv. Fix this by expanding the head whenever the remaining room is less than the push size plus mac_len, and request that much extra so the rebuilt MAC header fits afterwards.
CVE-2026-64216CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages() netfs_unlock_abandoned_read_pages(rreq) accesses the index of the folios it is wanting to unlock and compares that to rreq->no_unlock_folio so that it doesn't unlock a folio being read for netfs_perform_write() or netfs_write_begin(). However, given that netfs_unlock_abandoned_read_pages() is called _after_ NETFS_RREQ_IN_PROGRESS is cleared, the one folio that it's not allowed to dereference is the one specified by ->no_unlock_folio as ownership immediately reverts to the caller. Fix this by storing the folio pointer instead and using that rather than the index. Also fix netfs_unlock_read_folio() where the same applies.

References

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2026-43198. Free for 1 server.

Get started free