Vulnerability-Lookup

GHSA-CG8C-JGHV-84P9

Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33

Details

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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-72502"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-15T06:22:24Z",
    "severity": "HIGH"
  },
  "details": "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\".",
  "id": "GHSA-cg8c-jghv-84p9",
  "modified": "2026-08-17T06:33:34Z",
  "published": "2026-08-15T06:32:27Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72502"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/21f69ac1879bb970588d5e7c12a96e6542f7c1a7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/560b33b434e922ef97f9ff23aa2e909ef7aacd5c"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/572fff10819dfc359298d1f774839e76a4d96f93"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8e6214a530c03e341dc1b0a846c8f2b716b3551a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a210791f33345aa87187f7d7a9f3b9b7f4a28e6d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c0db3dc2ac323b6c4b76adede3b355a9daa6dea8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

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

Vulnerability from cvelistv5 – Published: 2026-08-15 05:57 – Updated: 2026-08-17 05:45

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

Linux mitre root

References

8 references

URL	Tags
https://git.kernel.org/stable/c/560b33b434e922ef9…
https://git.kernel.org/stable/c/21f69ac1879bb9705…
https://git.kernel.org/stable/c/c0db3dc2ac323b6c4…
https://git.kernel.org/stable/c/572fff10819dfc359…
https://git.kernel.org/stable/c/8e6214a530c03e341…
https://git.kernel.org/stable/c/d774cdbda6634a78d…
https://git.kernel.org/stable/c/a210791f33345aa87…
https://git.kernel.org/stable/c/2bf43d0e2e6a27d52…

Impacted products

2 products

Vendor	Product	Version
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)
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)

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{
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          "programFiles": [
            "net/ipv6/route.c"
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              "version": "4.8"
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              "status": "unaffected",
              "version": "0",
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              "status": "unaffected",
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              "versionType": "semver"
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              "versionType": "original_commit_for_fix"
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          "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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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
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            {
              "lang": "en",
              "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."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:45:02.121Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        {
          "url": "https://git.kernel.org/stable/c/2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22"
        }
      ],
      "title": "tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)",
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    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-72502",
    "datePublished": "2026-08-15T05:57:33.647Z",
    "dateReserved": "2026-08-09T03:40:39.938Z",
    "dateUpdated": "2026-08-17T05:45:02.121Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

GHSA-CG8C-JGHV-84P9

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

Tags

Sightings

Nomenclature