CVE-2026-64007netfilter: synproxy: refresh tcphdr after skb_ensure_writable
- 9.8CriticalCVSS base score
- 0.51%Exploitation in 30 daysEPSS · top 56% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
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.
Timeline
ID reserved
By Linux
Published
- 3 months later
· 3 months later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| LinuxCNA (assigner) | 3.1 | Critical9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| NVDNVD · Modified | 3.1 | Critical9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
- EPSS (exploitation in 30 days)
- 0.51% · top 56% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.8.
Affected products
- affected 48b1de4c110a7afa4b85862f6c75af817db26fad – < 9902a1058992de5d95656b64a3bd95c077f7ba2c
- affected 48b1de4c110a7afa4b85862f6c75af817db26fad – < d3019c61799adc21811af4b521f11f3dc77f8e04
- affected 48b1de4c110a7afa4b85862f6c75af817db26fad – < dd206819f210522579010d889d45a9530bb494bc
- affected 48b1de4c110a7afa4b85862f6c75af817db26fad – < af2c22ccb1f621aff487ff47a040e38e058541e7
- affected 48b1de4c110a7afa4b85862f6c75af817db26fad – < c7f945f7da097245a2f8ed7775ce48421047ee96
- affected 48b1de4c110a7afa4b85862f6c75af817db26fad – < f0fea2b6d5453a11ad11713bbf37561b9b3a7edf
- affected 48b1de4c110a7afa4b85862f6c75af817db26fad – < a91887a5b6ee4b98dfbf1db657ed2b879430149e
- affected 48b1de4c110a7afa4b85862f6c75af817db26fad – < 92170e6afe927ab2792a3f71902845789c8e31b1
- affected 3.12
- unaffected < 3.12
- unaffected 5.10.259 – ≤ 5.10.*
- unaffected 5.15.210 – ≤ 5.15.*
- unaffected 6.1.176 – ≤ 6.1.*
- unaffected 6.6.143 – ≤ 6.6.*
- unaffected 6.12.93 – ≤ 6.12.*
- unaffected 6.18.35 – ≤ 6.18.*
- unaffected 7.0.12 – ≤ 7.0.*
- unaffected 7.1 – ≤ *
References
References8
- https://git.kernel.org/stable/c/9902a1058992de5d95656b64a3bd95c077f7ba2c (opens in a new tab)
- https://git.kernel.org/stable/c/d3019c61799adc21811af4b521f11f3dc77f8e04 (opens in a new tab)
- https://git.kernel.org/stable/c/dd206819f210522579010d889d45a9530bb494bc (opens in a new tab)
- https://git.kernel.org/stable/c/af2c22ccb1f621aff487ff47a040e38e058541e7 (opens in a new tab)
- https://git.kernel.org/stable/c/c7f945f7da097245a2f8ed7775ce48421047ee96 (opens in a new tab)
- https://git.kernel.org/stable/c/f0fea2b6d5453a11ad11713bbf37561b9b3a7edf (opens in a new tab)
- https://git.kernel.org/stable/c/a91887a5b6ee4b98dfbf1db657ed2b879430149e (opens in a new tab)
- https://git.kernel.org/stable/c/92170e6afe927ab2792a3f71902845789c8e31b1 (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-45580 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
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[](https://cveledger.app/cve/CVE-2026-64007)Record last updated .