CVE-2026-64007netfilter: synproxy: refresh tcphdr after skb_ensure_writable
Updated under an hour ago ()
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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.
- CVSS
- 9.8 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- Not given
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Linux
- NVD analysis
- Analyzed
- Record last updated
- Oct 16, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Linux Linux linux:linux (from the name) | from 48b1de4c110a7afa4b85862f6c75af817db26fad before 9902a1058992de5d95656b64a3bd95c077f7ba2c; from 48b1de4c110a7afa4b85862f6c75af817db26fad before d3019c61799adc21811af4b521f11f3dc77f8e04; from 48b1de4c110a7afa4b85862f6c75af817db26fad before dd206819f210522579010d889d45a9530bb494bc; from 48b1de4c110a7afa4b85862f6c75af817db26fad before af2c22ccb1f621aff487ff47a040e38e058541e7; from 48b1de4c110a7afa4b85862f6c75af817db26fad before c7f945f7da097245a2f8ed7775ce48421047ee96; from 48b1de4c110a7afa4b85862f6c75af817db26fad before f0fea2b6d5453a11ad11713bbf37561b9b3a7edf; from 48b1de4c110a7afa4b85862f6c75af817db26fad before a91887a5b6ee4b98dfbf1db657ed2b879430149e; from 48b1de4c110a7afa4b85862f6c75af817db26fad before 92170e6afe927ab2792a3f71902845789c8e31b1 | CNA record |
linux linux_kernel linux:linux_kernel | from 3.12 before 5.10.259; from 5.11 before 5.15.210; from 5.16 before 6.1.176; from 6.2 before 6.6.143; from 6.7 before 6.12.93; from 6.13 before 6.18.35; from 6.19 before 7.0.12; 7.1; and 4 more ranges | NVD |
References
- https://git.kernel.org/stable/c/9902a1058992de5d95656b64a3bd95c077f7ba2cpatch
- https://git.kernel.org/stable/c/d3019c61799adc21811af4b521f11f3dc77f8e04patch
- https://git.kernel.org/stable/c/dd206819f210522579010d889d45a9530bb494bcpatch
- https://git.kernel.org/stable/c/af2c22ccb1f621aff487ff47a040e38e058541e7patch
- https://git.kernel.org/stable/c/c7f945f7da097245a2f8ed7775ce48421047ee96patch
- https://git.kernel.org/stable/c/f0fea2b6d5453a11ad11713bbf37561b9b3a7edfpatch
- https://git.kernel.org/stable/c/a91887a5b6ee4b98dfbf1db657ed2b879430149epatch
- https://git.kernel.org/stable/c/92170e6afe927ab2792a3f71902845789c8e31b1patch
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.