GHSA-CG8C-JGHV-84P9
Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33In 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".
{
"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"
}
]
}
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