critical CVSS 9.8

CVE-2026-43501·Kernel vulnerability

In 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.

Severity: critical
Software: Kernel
Fixed in: 7.0.4
Published: 2026-05-21

Affected versions

From: 6.19

Until: 7.0.4

Fixed in: 7.0.4

How to fix this CVE

Update your Linux kernel to version 7.0.4 or later to patch a critical memory corruption vulnerability in IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) header processing. This vulnerability allows unauthenticated remote attackers to trigger out-of-bounds memory writes through specially crafted IPv6 packets with type-3 Source Routing Headers. Immediate patching is strongly recommended for all systems, particularly those processing IPv6 traffic or running network services.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

Check current kernel version: uname -r; if output is between 6.19 and 7.0.3, the system is vulnerable
Verify IPv6 is enabled: cat /proc/sys/net/ipv6/conf/all/disable_ipv6; a value of 0 indicates IPv6 is active and the vulnerability surface exists
Search kernel logs for RPL-related errors: journalctl -b | grep -i 'rpl\|srh\|routing'; look for memory access violations or oops messages
Confirm patched kernel is installed: uname -r should show 7.0.4 or later; verify with grep 'rpl_srh' /boot/config-$(uname -r) to ensure RPL code is compiled in

FAQ

What is CVE-2026-43501?

CVE-2026-43501 is a critical kernel vulnerability in IPv6 RPL header processing where insufficient headroom validation during Source Routing Header recompression allows remote attackers to write memory outside allocated buffer boundaries, potentially causing kernel crashes or arbitrary code execution.

Is CVE-2026-43501 being actively exploited?

No. This vulnerability is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog and no public exploits are currently available, though the critical severity warrants urgent patching.

What versions of Kernel are affected by CVE-2026-43501?

Linux kernel versions 6.19 through 7.0.3 are vulnerable. Version 7.0.4 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-43501?

Run 'uname -r' and compare the output against the vulnerable range (6.19 to 7.0.3). If your kernel version falls within this range, your system is vulnerable.

Does Defensia detect CVE-2026-43501?

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-2026-43501 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-2026-43198CVSS 9.8In 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.

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-2026-64216CVSS 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

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