GHSA-RF6C-225M-P2P4
Vulnerability from github – Published: 2026-07-19 18:31 – Updated: 2026-07-20 15:31In the Linux kernel, the following vulnerability has been resolved:
netfilter: synproxy: refresh tcphdr after skb_ensure_writable
synproxy_tstamp_adjust() rewrites the TCP timestamp option in place and then patches the TCP checksum via inet_proto_csum_replace4() on the caller-supplied tcphdr pointer. Both ipv4_synproxy_hook() and ipv6_synproxy_hook() obtain that pointer with skb_header_pointer() before calling in, so it may either alias skb->head directly or point at the caller's on-stack _tcph buffer.
Between obtaining the pointer and using it, the function calls skb_ensure_writable(skb, optend), which on a cloned or non-linear skb invokes pskb_expand_head() and frees the old skb->head. After that point the cached th is stale:
caller (ipv[46]_synproxy_hook)
th = skb_header_pointer(skb, ..., &_tcph)
synproxy_tstamp_adjust(skb, protoff, th, ...)
skb_ensure_writable(skb, optend)
pskb_expand_head() /* kfree(old skb->head) */
...
inet_proto_csum_replace4(&th->check, ...)
/* writes into freed head, or
into the caller's stack copy
leaving the on-wire checksum
stale */
The option bytes are written through skb->data and are fine; only the checksum update goes through th and so lands in the wrong place. The result is either a write into freed slab memory or a packet leaving with a checksum that does not match its payload.
Fix by re-deriving th from skb->data + protoff immediately after skb_ensure_writable() succeeds, so the subsequent checksum update targets the linear, writable header.
{
"affected": [],
"aliases": [
"CVE-2026-64007"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-19T16:17:40Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: synproxy: refresh tcphdr after skb_ensure_writable\n\nsynproxy_tstamp_adjust() rewrites the TCP timestamp option in place\nand then patches the TCP checksum via inet_proto_csum_replace4() on\nthe caller-supplied tcphdr pointer. Both ipv4_synproxy_hook() and\nipv6_synproxy_hook() obtain that pointer with skb_header_pointer()\nbefore calling in, so it may either alias skb-\u003ehead directly or\npoint at the caller\u0027s on-stack _tcph buffer.\n\nBetween obtaining the pointer and using it, the function calls\nskb_ensure_writable(skb, optend), which on a cloned or non-linear\nskb invokes pskb_expand_head() and frees the old skb-\u003ehead. After\nthat point the cached th is stale:\n\n caller (ipv[46]_synproxy_hook)\n th = skb_header_pointer(skb, ..., \u0026_tcph)\n synproxy_tstamp_adjust(skb, protoff, th, ...)\n skb_ensure_writable(skb, optend)\n pskb_expand_head() /* kfree(old skb-\u003ehead) */\n ...\n inet_proto_csum_replace4(\u0026th-\u003echeck, ...)\n /* writes into freed head, or\n into the caller\u0027s stack copy\n leaving the on-wire checksum\n stale */\n\nThe option bytes are written through skb-\u003edata and are fine; only\nthe checksum update goes through th and so lands in the wrong\nplace. The result is either a write into freed slab memory or a\npacket leaving with a checksum that does not match its payload.\n\nFix by re-deriving th from skb-\u003edata + protoff immediately after\nskb_ensure_writable() succeeds, so the subsequent checksum update\ntargets the linear, writable header.",
"id": "GHSA-rf6c-225m-p2p4",
"modified": "2026-07-20T15:31:55Z",
"published": "2026-07-19T18:31:49Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64007"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/92170e6afe927ab2792a3f71902845789c8e31b1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9902a1058992de5d95656b64a3bd95c077f7ba2c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a91887a5b6ee4b98dfbf1db657ed2b879430149e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/af2c22ccb1f621aff487ff47a040e38e058541e7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c7f945f7da097245a2f8ed7775ce48421047ee96"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d3019c61799adc21811af4b521f11f3dc77f8e04"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/dd206819f210522579010d889d45a9530bb494bc"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f0fea2b6d5453a11ad11713bbf37561b9b3a7edf"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Confirmed: The vulnerability has been validated from an analyst's perspective.
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- 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.