tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)

{
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  "url": "https://osv.dev/vulnerability/CVE-2026-72502",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF) When MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535). This is interpreted by TCP as mss_clamp, allowing the MSS to reach 65535. However, 0xFFFF is also used as a magic value GSO_BY_FRAGS in the kernel. If a TCP packet with gso_size=0xFFFF is passed to skb_segment(), it will be mistakenly treated as GSO_BY_FRAGS, leading to a NULL pointer dereference because local TCP packets do not use frag_list. Fix this by returning min(IPV6_MAXPLEN, GSO_BY_FRAGS - 1) (65534) from ip6_default_advmss() when MTU is large. Also update the stale comment in ip6_default_advmss() which suggested that IPV6_MAXPLEN is returned to mean \"any MSS\".",
    "evidence": "osv:CVE-2026-72502",
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      "modified": "2026-10-28T02:30:32.311656169Z",
      "provider": "osv",
      "references": [
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  "source_id": "core-osv",
  "document_id": 499599,
  "published_at": "2026-08-15T05:57:33.647+00:00"
}