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GHSA-M3F3-9J4Q-C4F2

Vulnerability from github – Published: 2026-09-04 18:31 – Updated: 2026-09-11 12:33
VLAI
Details

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.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-80847"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-04T16:18:13Z",
    "severity": null
  },
  "details": "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.",
  "id": "GHSA-m3f3-9j4q-c4f2",
  "modified": "2026-09-11T12:33:24Z",
  "published": "2026-09-04T18:31:28Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80847"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/31cf2349361902769dc323e4dbf4b449795ec288"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6b8c20bf61924dfc38fefb145c9f7406d73fae53"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/cfb44c6028e6f979720315e0772bbd0d4d33ed61"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}



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