tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 6.12.114, 6.18.34, 7.0.11
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: yes
- Technical impact: partial
Summary
In the Linux kernel, the following vulnerability has been resolved: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction Blamed commit moved the TIME_WAIT-derived ISN from the skb control block to a per-CPU variable, assuming the value would always be consumed by tcp_conn_request() for the same packet that wrote it. That assumption is violated by multiple drop paths between the producer (__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer (tcp_conn_request()): • min_ttl / min_hopcount check • xfrm policy check • tcp_inbound_hash() MD5/AO mismatch • tcp_filter() eBPF/SO_ATTACH_FILTER drop • th->syn && th->fin discard in tcp_rcv_state_process() TCP_LISTEN • psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv() • tcp_checksum_complete() in tcp_v{4,6}_do_rcv() • tcp_v{4,6}_cookie_check() returning NULL When a packet is dropped on any of these paths, tcp_tw_isn is left set. The next SYN processed on the same CPU then consumes the non zero value in tcp_conn_request(), receiving a potentially predictable ISN. This patch moves back tcp_tw_isn to skb->cb[], getting rid of the per-cpu variable. Note that tcp_v{4,6}_fill_cb() do not set it. Very litle impact on overall code size/complexity: $ scripts/bloat-o-meter -t vmlinux.old vmlinux.new add/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7) Function old new delta tcp_v6_rcv 3038 3042 +4 tcp_v4_rcv 3035 3039 +4 tcp_conn_request 2938 2923 -15 Total: Before=24436060, After=24436053, chg -0.00%
Timeline
- CVE published
- CISA SSVC assessment
Exploitation: none · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- Linux Linux
From 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 · fixed in 8bb6aa419b142dcc2680177ecc39c4c38db7fc16; From 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 · fixed in e47f7060eaf60894e3e4d0e3c4fe6e1f2eacfbdd; From 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 · fixed in 4affe063fa56c880cbea8d0bfded0bb80751579d; From 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 · fixed in 1bbf0ced1d9db73ac7893c2187f3459288603e0d
- Linux Linux
6.10
- KernelLinux
From 6.10.0 · fixed in 6.12.114; From 6.13.0 · fixed in 6.18.34; From 6.19.0 · fixed in 7.0.11