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CVE-2026-64007

netfilter: synproxy: refresh tcphdr after skb_ensure_writable

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: yes
  • Technical impact: total

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: yes · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From 48b1de4c110a7afa4b85862f6c75af817db26fad · fixed in 9902a1058992de5d95656b64a3bd95c077f7ba2c; From 48b1de4c110a7afa4b85862f6c75af817db26fad · fixed in d3019c61799adc21811af4b521f11f3dc77f8e04; From 48b1de4c110a7afa4b85862f6c75af817db26fad · fixed in dd206819f210522579010d889d45a9530bb494bc; From 48b1de4c110a7afa4b85862f6c75af817db26fad · fixed in af2c22ccb1f621aff487ff47a040e38e058541e7; From 48b1de4c110a7afa4b85862f6c75af817db26fad · fixed in c7f945f7da097245a2f8ed7775ce48421047ee96; From 48b1de4c110a7afa4b85862f6c75af817db26fad · fixed in f0fea2b6d5453a11ad11713bbf37561b9b3a7edf; From 48b1de4c110a7afa4b85862f6c75af817db26fad · fixed in a91887a5b6ee4b98dfbf1db657ed2b879430149e; From 48b1de4c110a7afa4b85862f6c75af817db26fad · fixed in 92170e6afe927ab2792a3f71902845789c8e31b1

  • Linux Linux

    3.12

  • KernelLinux

    From 3.12.0 · fixed in 5.10.259; From 5.11.0 · fixed in 5.15.210; From 5.16.0 · fixed in 6.1.176; From 6.2.0 · fixed in 6.6.143; From 6.7.0 · fixed in 6.12.93; From 6.13.0 · fixed in 6.18.35; From 6.19.0 · fixed in 7.0.12

References 8

git.kernel.org