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CVE-2026-80847 (GCVE-0-2026-80847)

Vulnerability from cvelistv5 – Published: 2026-09-04 15:54 – Updated: 2026-09-11 09:57
VLAI
Title
tcp: clamp route advmss to TCP_MIN_MSS
Summary
In the Linux kernel, the following vulnerability has been resolved: tcp: clamp route advmss to TCP_MIN_MSS tcp_select_initial_window() assumes that callers never pass an MSS smaller than 1, but route-derived advmss values can violate that assumption. A too-small explicit RTAX_ADVMSS is one way to get there, but it is not the only one. The same divide-by-zero can also be reached through the "default advmss" path when RTAX_ADVMSS is left at 0 and the effective advmss is later driven down by route MTU and min_adv_mss. Introduce a tcp_dst_advmss() helper that clamps route advmss to TCP_MIN_MSS before TCP consumes it, and use it in the TCP paths that derive advmss from dst metrics. This keeps the effective MSS from dropping to zero before tcp_select_initial_window() rounds the receive window.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < cfb44c6028e6f979720315e0772bbd0d4d33ed61 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 6b8c20bf61924dfc38fefb145c9f7406d73fae53 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 31cf2349361902769dc323e4dbf4b449795ec288 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 6.18.51 , ≤ 6.18.* (semver)
Unaffected: 7.1.13 , ≤ 7.1.* (semver)
Unaffected: 7.2.3 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/tcp.h",
            "net/ipv4/tcp_ipv4.c",
            "net/ipv4/tcp_minisocks.c",
            "net/ipv4/tcp_output.c",
            "net/ipv6/tcp_ipv6.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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            "net/ipv6/tcp_ipv6.c"
          ],
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          "vendor": "Linux",
          "versions": [
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              "status": "unaffected",
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              "versionType": "semver"
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              "status": "unaffected",
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      ],
      "cpeApplicability": [
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          "nodes": [
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: clamp route advmss to TCP_MIN_MSS\n\ntcp_select_initial_window() assumes that callers never pass an MSS\nsmaller than 1, but route-derived advmss values can violate that\nassumption.\n\nA too-small explicit RTAX_ADVMSS is one way to get there, but it is not\nthe only one. The same divide-by-zero can also be reached through the\n\"default advmss\" path when RTAX_ADVMSS is left at 0 and the effective\nadvmss is later driven down by route MTU and min_adv_mss.\n\nIntroduce a tcp_dst_advmss() helper that clamps route advmss to\nTCP_MIN_MSS before TCP consumes it, and use it in the TCP paths that\nderive advmss from dst metrics. This keeps the effective MSS from\ndropping to zero before tcp_select_initial_window() rounds the receive\nwindow."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-11T09:57:09.499Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/cfb44c6028e6f979720315e0772bbd0d4d33ed61"
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        },
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          "url": "https://git.kernel.org/stable/c/870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1"
        }
      ],
      "title": "tcp: clamp route advmss to TCP_MIN_MSS",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-80847",
    "datePublished": "2026-09-04T15:54:57.441Z",
    "dateReserved": "2026-08-26T14:34:25.797Z",
    "dateUpdated": "2026-09-11T09:57:09.499Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
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      "date": "2026-09-14",
      "epss": "0.00168",
      "percentile": "0.06391"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-07T01:52:27.000Z",
      "cve": "CVE-2026-80847",
      "id": "msrc_CVE-2026-80847",
      "initial_release_date": "2026-09-07T01:52:27.000Z",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "tcp: clamp route advmss to TCP_MIN_MSS",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-80847.json",
      "version": "1"
    },
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    "suse_vex": {
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      "current_release_date": "2026-09-10T01:50:39Z",
      "cve": "CVE-2026-80847",
      "id": "CVE-2026-80847",
      "initial_release_date": "2026-09-05T00:26:17Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-80847",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-80847.json",
      "version": "4"
    }
  }
}



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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.

Sightings

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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.


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