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

Type: advisorySource: Official CVE List1 source record

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_

Announced Source revision 1
Original source ↗

CVE-2026-97984

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-97984

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
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Prerequisites
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Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "427faee167bce4ccb0b22f6815a9ac509e31d4c3",
        "lessThan": "1dd562f3019019ffdf4b396570613053facda9ee",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "427faee167bce4ccb0b22f6815a9ac509e31d4c3",
        "lessThan": "1d56a00ec91f2885c64ea5b8cea18cb746b91bbb",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "427faee167bce4ccb0b22f6815a9ac509e31d4c3",
        "lessThan": "ce66352d3eb21825410af8b91db7cc4bb8e22c98",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "427faee167bce4ccb0b22f6815a9ac509e31d4c3",
        "lessThan": "e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "427faee167bce4ccb0b22f6815a9ac509e31d4c3",
        "lessThan": "0ae10b6be49b425827659b23bcce498f80eb7182",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "net/ipv6/ip6_output.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "5.15"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "5.15",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "6.6.158",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.111",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.53",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.2.7",
        "versionType": "semver",
        "lessThanOrEqual": "7.2.*"
      },
      {
        "status": "unaffected",
        "version": "7.3",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "net/ipv6/ip6_output.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-97984

Source reference: /cveMetadata/cveId

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Event
#38118 · Revision 1
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