# CVE-2026-98802: seg6: ensure packet data is writable before modifying SRH and IPv6 DA

CVE-2026-98802 is fixed in linux on 1 platform by DEBIAN-CVE-2026-98802 (version 7.2.10-1), released October 19, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98802
- Priority: Routine
- CVSS: 3.7 (Low)
- EPSS: 0.0016
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 18, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98802

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.2.10-1 | [DEBIAN-CVE-2026-98802](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98802.md) | Oct 19, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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