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CVE-2026-72502 (GCVE-0-2026-72502)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:57 – Updated: 2026-08-17 05:45
VLAI
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".
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 3953c46c3ac7eef31a9935427371c6f54a22f1ba , < 560b33b434e922ef97f9ff23aa2e909ef7aacd5c (git)
Affected: 3953c46c3ac7eef31a9935427371c6f54a22f1ba , < 21f69ac1879bb970588d5e7c12a96e6542f7c1a7 (git)
Affected: 3953c46c3ac7eef31a9935427371c6f54a22f1ba , < c0db3dc2ac323b6c4b76adede3b355a9daa6dea8 (git)
Affected: 3953c46c3ac7eef31a9935427371c6f54a22f1ba , < 572fff10819dfc359298d1f774839e76a4d96f93 (git)
Affected: 3953c46c3ac7eef31a9935427371c6f54a22f1ba , < 8e6214a530c03e341dc1b0a846c8f2b716b3551a (git)
Affected: 3953c46c3ac7eef31a9935427371c6f54a22f1ba , < d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e (git)
Affected: 3953c46c3ac7eef31a9935427371c6f54a22f1ba , < a210791f33345aa87187f7d7a9f3b9b7f4a28e6d (git)
Affected: 3953c46c3ac7eef31a9935427371c6f54a22f1ba , < 2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22 (git)
guessed Create a notification for this product.
Linux Linux Affected: 4.8
Unaffected: 0 , < 4.8 (semver)
Unaffected: 5.10.261 , ≤ 5.10.* (semver)
Unaffected: 5.15.212 , ≤ 5.15.* (semver)
Unaffected: 6.1.178 , ≤ 6.1.* (semver)
Unaffected: 6.6.145 , ≤ 6.6.* (semver)
Unaffected: 6.12.97 , ≤ 6.12.* (semver)
Unaffected: 6.18.40 , ≤ 6.18.* (semver)
Unaffected: 7.1.5 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)\n\nWhen MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535).\nThis is interpreted by TCP as mss_clamp, allowing the MSS to reach 65535.\n\nHowever, 0xFFFF is also used as a magic value GSO_BY_FRAGS in the kernel.\nIf a TCP packet with gso_size=0xFFFF is passed to skb_segment(), it will\nbe mistakenly treated as GSO_BY_FRAGS, leading to a NULL pointer\ndereference because local TCP packets do not use frag_list.\n\nFix this by returning min(IPV6_MAXPLEN, GSO_BY_FRAGS - 1) (65534) from\nip6_default_advmss() when MTU is large.\n\nAlso update the stale comment in ip6_default_advmss() which suggested\nthat IPV6_MAXPLEN is returned to mean \"any MSS\"."
        }
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              "value": "AV:N - Reachable from the network via IPv6 TCP: a remote peer sends a crafted SYN (MSS=65535) or connects over a large-MTU IPv6 route, causing outbound TCP GSO skbs with gso_size=0xFFFF to be software-segmented in skb_segment() during normal packet transmit.\nAC:L - The attacker controls the TCP handshake MSS option and can induce \u003e64KB outbound segments; syzbot reproduced this reliably, and software GSO paths (loopback, veth, NETIF_F_GSO_SOFTWARE) are common in cloud/container deployments where skb_segment() is invoked.\nPR:N - No privileges are required; exploitation occurs on the pre-authentication passive-open path where the kernel accepts a remote TCP SYN and MSS option before any application-level authentication.\nUI:N - No victim user interaction is needed beyond the target system normally accepting IPv6 TCP connections and transmitting response data to the attacker-controlled peer.\nS:U - The vulnerability causes a kernel crash on the attacked host itself; it does not cross a security boundary such as a VM escape, container sandbox breakout, or IOMMU/DMA isolation bypass.\nC:N - Impact is a NULL pointer dereference in skb_segment() when gso_size equals GSO_BY_FRAGS; there is no out-of-bounds read, use-after-free, or other memory disclosure primitive.\nI:N - The bug does not corrupt or modify attacker-controlled memory; it dereferences a NULL frag_list pointer during segmentation, yielding a crash rather than a write or code-execution primitive.\nA:H - The NULL pointer dereference in skb_segment() triggers a kernel oops/panic, causing complete loss of availability for the affected system when the malicious IPv6 TCP traffic path is exercised."
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        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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    "dateReserved": "2026-08-09T03:40:39.938Z",
    "dateUpdated": "2026-08-17T05:45:02.121Z",
    "state": "PUBLISHED"
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update the stale comment in ip6_default_advmss() which suggested\\nthat IPV6_MAXPLEN is returned to mean \\\"any 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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-19T19:39:16+00:00",
      "cve": "CVE-2026-72502",
      "id": "CVE-2026-72502",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:known_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-72502.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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