Vulnerability-Lookup

GHSA-5M3W-7WWR-WQM2

Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 12:31

Details

In the Linux kernel, the following vulnerability has been resolved:

net: ipv6: Fix UDP length overflow with PMTU discover and big MTU

This commit bounds cork->base.fragsize to IP6_MAX_MTU for UDP sockets to avoid a possible overflow of UDP length that triggers a WARN in udp_set_len_short when setsockopt IPV6_MTU_DISCOVER is set to IPV6_PMTUDISC_DO or IPV6_PMTUDISC_PROBE, and a large packet is sent over a netdev with an unusually large MTU.

Steps to reproduce (included in the new selftest):

Set device MTU bigger than IP6_MAX_MTU. cork->base.fragsize will be set to that MTU in ip6_setup_cork.
Set IPV6_MTU_DISCOVER to IPV6_PMTUDISC_PROBE or IPV6_PMTUDISC_DO. It lets maxnonfragsize be set to device MTU (cork->fragsize) in __ip6_append_data, rather than to IP6_MAX_MTU.
Send 65528 bytes of payload (+8 bytes of UDP header, +40 bytes of IPv6 header). Device MTU allows it (it's only one byte bigger than IP6_MAX_MTU, and the device MTU is bigger than that).
The UDP length in the built packet is 65536, which overflows the 16-bit length field and triggers the WARN in udp_set_len_short.

To avoid breaking sending UDP jumbograms over raw IPv6 sockets, limit the change to UDP sockets only.

The original overflow bug with IPv6 and IPV6_PMTUDISC_DO seems to predate git history (verified reproduction on 2.6.21), was fixed later, and then reappeared in commit 427faee167bc ("net: ipv6: introduce ip6_dst_mtu_maybe_forward"), which is chosen as the Fixes tag here. The overflow with IPV6_PMTUDISC_PROBE reproduces since its introduction in commit 628a5c561890 ("[INET]: Add IP(V6)_PMTUDISC_RPOBE").

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{
  "affected": [],
  "aliases": [
    "CVE-2026-97984"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-25T11:17:26Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: Fix UDP length overflow with PMTU discover and big MTU\n\nThis commit bounds cork-\u003ebase.fragsize to IP6_MAX_MTU for UDP sockets to\navoid a possible overflow of UDP length that triggers a WARN in\nudp_set_len_short when setsockopt IPV6_MTU_DISCOVER is set to\nIPV6_PMTUDISC_DO or IPV6_PMTUDISC_PROBE, and a large packet is sent over\na netdev with an unusually large MTU.\n\nSteps to reproduce (included in the new selftest):\n\n1. Set device MTU bigger than IP6_MAX_MTU. cork-\u003ebase.fragsize will be\n   set to that MTU in ip6_setup_cork.\n2. Set IPV6_MTU_DISCOVER to IPV6_PMTUDISC_PROBE or IPV6_PMTUDISC_DO. It\n   lets maxnonfragsize be set to device MTU (cork-\u003efragsize) in\n   __ip6_append_data, rather than to IP6_MAX_MTU.\n3. Send 65528 bytes of payload (+8 bytes of UDP header, +40 bytes of\n   IPv6 header). Device MTU allows it (it\u0027s only one byte bigger than\n   IP6_MAX_MTU, and the device MTU is bigger than that).\n4. The UDP length in the built packet is 65536, which overflows the\n   16-bit length field and triggers the WARN in udp_set_len_short.\n\nTo avoid breaking sending UDP jumbograms over raw IPv6 sockets, limit\nthe change to UDP sockets only.\n\nThe original overflow bug with IPv6 and IPV6_PMTUDISC_DO seems to\npredate git history (verified reproduction on 2.6.21), was fixed later,\nand then reappeared in commit 427faee167bc (\"net: ipv6: introduce\nip6_dst_mtu_maybe_forward\"), which is chosen as the Fixes tag here. The\noverflow with IPV6_PMTUDISC_PROBE reproduces since its introduction in\ncommit 628a5c561890 (\"[INET]: Add IP(V6)_PMTUDISC_RPOBE\").",
  "id": "GHSA-5m3w-7wwr-wqm2",
  "modified": "2026-09-25T12:31:31Z",
  "published": "2026-09-25T12:31:31Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-97984"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0ae10b6be49b425827659b23bcce498f80eb7182"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1d56a00ec91f2885c64ea5b8cea18cb746b91bbb"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ce66352d3eb21825410af8b91db7cc4bb8e22c98"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-97984 (GCVE-0-2026-97984)

Vulnerability from cvelistv5 – Published: 2026-09-25 10:23 – Updated: 2026-09-25 10:23

Title

net: ipv6: Fix UDP length overflow with PMTU discover and big MTU

Summary

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: Fix UDP length overflow with PMTU discover and big MTU This commit bounds cork->base.fragsize to IP6_MAX_MTU for UDP sockets to avoid a possible overflow of UDP length that triggers a WARN in udp_set_len_short when setsockopt IPV6_MTU_DISCOVER is set to IPV6_PMTUDISC_DO or IPV6_PMTUDISC_PROBE, and a large packet is sent over a netdev with an unusually large MTU. Steps to reproduce (included in the new selftest): 1. Set device MTU bigger than IP6_MAX_MTU. cork->base.fragsize will be set to that MTU in ip6_setup_cork. 2. Set IPV6_MTU_DISCOVER to IPV6_PMTUDISC_PROBE or IPV6_PMTUDISC_DO. It lets maxnonfragsize be set to device MTU (cork->fragsize) in __ip6_append_data, rather than to IP6_MAX_MTU. 3. Send 65528 bytes of payload (+8 bytes of UDP header, +40 bytes of IPv6 header). Device MTU allows it (it's only one byte bigger than IP6_MAX_MTU, and the device MTU is bigger than that). 4. The UDP length in the built packet is 65536, which overflows the 16-bit length field and triggers the WARN in udp_set_len_short. To avoid breaking sending UDP jumbograms over raw IPv6 sockets, limit the change to UDP sockets only. The original overflow bug with IPv6 and IPV6_PMTUDISC_DO seems to predate git history (verified reproduction on 2.6.21), was fixed later, and then reappeared in commit 427faee167bc ("net: ipv6: introduce ip6_dst_mtu_maybe_forward"), which is chosen as the Fixes tag here. The overflow with IPV6_PMTUDISC_PROBE reproduces since its introduction in commit 628a5c561890 ("[INET]: Add IP(V6)_PMTUDISC_RPOBE").

Severity

No CVSS data available.

Assigner

Linux mitre root

References

4 references

URL	Tags
https://git.kernel.org/stable/c/1d56a00ec91f2885c…
https://git.kernel.org/stable/c/ce66352d3eb218254…
https://git.kernel.org/stable/c/e01b7c176d9af2b7c…
https://git.kernel.org/stable/c/0ae10b6be49b42582…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 427faee167bce4ccb0b22f6815a9ac509e31d4c3 , < 1d56a00ec91f2885c64ea5b8cea18cb746b91bbb (git) Affected: 427faee167bce4ccb0b22f6815a9ac509e31d4c3 , < ce66352d3eb21825410af8b91db7cc4bb8e22c98 (git) Affected: 427faee167bce4ccb0b22f6815a9ac509e31d4c3 , < e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc (git) Affected: 427faee167bce4ccb0b22f6815a9ac509e31d4c3 , < 0ae10b6be49b425827659b23bcce498f80eb7182 (git)
Linux	Linux	Affected: 5.15 Unaffected: 0 , < 5.15 (semver) Unaffected: 6.12.111 , ≤ 6.12.* (semver) Unaffected: 6.18.53 , ≤ 6.18.* (semver) Unaffected: 7.2.7 , ≤ 7.2.* (semver) Unaffected: 7.3-rc3 , ≤ * (original_commit_for_fix)

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        {
          "defaultStatus": "unaffected",
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            {
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              "versionType": "semver"
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              "versionType": "semver"
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              "status": "unaffected",
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              "versionType": "semver"
            },
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    "dateReserved": "2026-09-25T10:18:58.208Z",
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}

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.

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.
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GHSA-5M3W-7WWR-WQM2

CVE-2026-97984 (GCVE-0-2026-97984)

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