CVE-2026-64007 (GCVE-0-2026-64007)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:56 – Updated: 2026-07-20 13:42
VLAI
Title
netfilter: synproxy: refresh tcphdr after skb_ensure_writable
Summary
In 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.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 48b1de4c110a7afa4b85862f6c75af817db26fad , < 9902a1058992de5d95656b64a3bd95c077f7ba2c (git)
Affected: 48b1de4c110a7afa4b85862f6c75af817db26fad , < d3019c61799adc21811af4b521f11f3dc77f8e04 (git)
Affected: 48b1de4c110a7afa4b85862f6c75af817db26fad , < dd206819f210522579010d889d45a9530bb494bc (git)
Affected: 48b1de4c110a7afa4b85862f6c75af817db26fad , < af2c22ccb1f621aff487ff47a040e38e058541e7 (git)
Affected: 48b1de4c110a7afa4b85862f6c75af817db26fad , < c7f945f7da097245a2f8ed7775ce48421047ee96 (git)
Affected: 48b1de4c110a7afa4b85862f6c75af817db26fad , < f0fea2b6d5453a11ad11713bbf37561b9b3a7edf (git)
Affected: 48b1de4c110a7afa4b85862f6c75af817db26fad , < a91887a5b6ee4b98dfbf1db657ed2b879430149e (git)
Affected: 48b1de4c110a7afa4b85862f6c75af817db26fad , < 92170e6afe927ab2792a3f71902845789c8e31b1 (git)
Create a notification for this product.
Linux Linux Affected: 3.12
Unaffected: 0 , < 3.12 (semver)
Unaffected: 5.10.259 , ≤ 5.10.* (semver)
Unaffected: 5.15.210 , ≤ 5.15.* (semver)
Unaffected: 6.1.176 , ≤ 6.1.* (semver)
Unaffected: 6.6.143 , ≤ 6.6.* (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
Create a notification for this product.
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      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
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            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
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      "providerMetadata": {
        "dateUpdated": "2026-07-20T13:42:17.862Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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    "dateReserved": "2026-07-19T07:54:57.026Z",
    "dateUpdated": "2026-07-20T13:42:17.862Z",
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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.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"net/netfilter/nf_synproxy_core.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"48b1de4c110a7afa4b85862f6c75af817db26fad\",\"lessThan\":\"9902a1058992de5d95656b64a3bd95c077f7ba2c\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"48b1de4c110a7afa4b85862f6c75af817db26fad\",\"lessThan\":\"d3019c61799adc21811af4b521f11f3dc77f8e04\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"48b1de4c110a7afa4b85862f6c75af817db26fad\",\"lessThan\":\"dd206819f210522579010d889d45a9530bb494bc\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"48b1de4c110a7afa4b85862f6c75af817db26fad\",\"lessThan\":\"af2c22ccb1f621aff487ff47a040e38e058541e7\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"48b1de4c110a7afa4b85862f6c75af817db26fad\",\"lessThan\":\"c7f945f7da097245a2f8ed7775ce48421047ee96\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"48b1de4c110a7afa4b85862f6c75af817db26fad\",\"lessThan\":\"f0fea2b6d5453a11ad11713bbf37561b9b3a7edf\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"48b1de4c110a7afa4b85862f6c75af817db26fad\",\"lessThan\":\"a91887a5b6ee4b98dfbf1db657ed2b879430149e\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"48b1de4c110a7afa4b85862f6c75af817db26fad\",\"lessThan\":\"92170e6afe927ab2792a3f71902845789c8e31b1\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"net/netfilter/nf_synproxy_core.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"3.12\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"3.12\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.10.259\",\"lessThanOrEqual\":\"5.10.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.210\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.1.176\",\"lessThanOrEqual\":\"6.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.143\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.93\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.35\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.0.12\",\"lessThanOrEqual\":\"7.0.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":9.8,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":5.9}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/92170e6afe927ab2792a3f71902845789c8e31b1\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/9902a1058992de5d95656b64a3bd95c077f7ba2c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a91887a5b6ee4b98dfbf1db657ed2b879430149e\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/af2c22ccb1f621aff487ff47a040e38e058541e7\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/c7f945f7da097245a2f8ed7775ce48421047ee96\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/d3019c61799adc21811af4b521f11f3dc77f8e04\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/dd206819f210522579010d889d45a9530bb494bc\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/f0fea2b6d5453a11ad11713bbf37561b9b3a7edf\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}



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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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  • 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.
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