In the Linux kernel, the following vulnerability has been resolved:
seg6: ensure packet data is writable before modifying SRH and IPv6 DA
advance_nextseg() modifies the SRH Segments Left field and the IPv6
destination address without ensuring the packet data is writable.
seg6_next_csid_advance_arg() has the same problem when it advances the
NEXT-C-SID argument in the destination address.
The skb may be cloned, for example by an AF_PACKET socket receiving on
the ingress device. advance_nextseg() and seg6_next_csid_advance_arg()
then write into the packet data shared with the clone. A read from that
socket can return the modified packet instead of the received one. The
simplified path below shows this for advance_nextseg():
__netif_receive_skb_one_core
__netif_receive_skb_core
deliver_skb [orig: users=2, cloned=0]
packet_rcv
skb_clone clone queued to the AF_PACKET socket
consume_skb(orig) [orig: users=1, cloned=1]
ipv6_rcv
ip6_rcv_core skb_share_check: no-op [orig: users=1]
[...]
input_action_end_core
advance_nextseg writes into the data shared with the clone
Call skb_ensure_writable() in advance_nextseg() and in
seg6_next_csid_advance_arg() before they modify the packet data.
skb_ensure_writable() may reallocate skb->head, which invalidates the
pointers into the packet data taken before the call.
advance_nextseg() now returns a valid SRH pointer, or NULL if
skb_ensure_writable() fails.
seg6_next_csid_advance_arg() takes the pointer to the destination
address from the skb after skb_ensure_writable().
On failure, the callers drop the packet with SKB_DROP_REASON_NOMEM.
seg6: ensure packet data is writable before modifying SRH and IPv6 DA
advance_nextseg() modifies the SRH Segments Left field and the IPv6
destination address without ensuring the packet data is writable.
seg6_next_csid_advance_arg() has the same problem when it advances the
NEXT-C-SID argument in the destination address.
The skb may be cloned, for example by an AF_PACKET socket receiving on
the ingress device. advance_nextseg() and seg6_next_csid_advance_arg()
then write into the packet data shared with the clone. A read from that
socket can return the modified packet instead of the received one. The
simplified path below shows this for advance_nextseg():
__netif_receive_skb_one_core
__netif_receive_skb_core
deliver_skb [orig: users=2, cloned=0]
packet_rcv
skb_clone clone queued to the AF_PACKET socket
consume_skb(orig) [orig: users=1, cloned=1]
ipv6_rcv
ip6_rcv_core skb_share_check: no-op [orig: users=1]
[...]
input_action_end_core
advance_nextseg writes into the data shared with the clone
Call skb_ensure_writable() in advance_nextseg() and in
seg6_next_csid_advance_arg() before they modify the packet data.
skb_ensure_writable() may reallocate skb->head, which invalidates the
pointers into the packet data taken before the call.
advance_nextseg() now returns a valid SRH pointer, or NULL if
skb_ensure_writable() fails.
seg6_next_csid_advance_arg() takes the pointer to the destination
address from the skb after skb_ensure_writable().
On failure, the callers drop the packet with SKB_DROP_REASON_NOMEM.
Metrics
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Fixes
Solution
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Workaround
No workaround given by the vendor.
References
History
Sun, 18 Oct 2026 16:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: seg6: ensure packet data is writable before modifying SRH and IPv6 DA advance_nextseg() modifies the SRH Segments Left field and the IPv6 destination address without ensuring the packet data is writable. seg6_next_csid_advance_arg() has the same problem when it advances the NEXT-C-SID argument in the destination address. The skb may be cloned, for example by an AF_PACKET socket receiving on the ingress device. advance_nextseg() and seg6_next_csid_advance_arg() then write into the packet data shared with the clone. A read from that socket can return the modified packet instead of the received one. The simplified path below shows this for advance_nextseg(): __netif_receive_skb_one_core __netif_receive_skb_core deliver_skb [orig: users=2, cloned=0] packet_rcv skb_clone clone queued to the AF_PACKET socket consume_skb(orig) [orig: users=1, cloned=1] ipv6_rcv ip6_rcv_core skb_share_check: no-op [orig: users=1] [...] input_action_end_core advance_nextseg writes into the data shared with the clone Call skb_ensure_writable() in advance_nextseg() and in seg6_next_csid_advance_arg() before they modify the packet data. skb_ensure_writable() may reallocate skb->head, which invalidates the pointers into the packet data taken before the call. advance_nextseg() now returns a valid SRH pointer, or NULL if skb_ensure_writable() fails. seg6_next_csid_advance_arg() takes the pointer to the destination address from the skb after skb_ensure_writable(). On failure, the callers drop the packet with SKB_DROP_REASON_NOMEM. | |
| Title | seg6: ensure packet data is writable before modifying SRH and IPv6 DA | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-18T15:48:49.192Z
Reserved: 2026-09-25T10:25:14.371Z
Link: CVE-2026-98802
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-18T16:17:34.250
Modified: 2026-10-18T16:17:34.250
Link: CVE-2026-98802
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.