# CVE-2026-45841: netfilter: nfnetlink_osf: fix divide-by-zero in OSF_WSS_MODULO

Status: published. Published: 2026-05-27. Updated: 2026-11-06.

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nfnetlink_osf: fix divide-by-zero in OSF_WSS_MODULO

nf_osf_match_one() computes ctx->window % f->wss.val in the
OSF_WSS_MODULO branch with no guard for f->wss.val == 0. A
CAP_NET_ADMIN user can add such a fingerprint via nfnetlink; a
subsequent matching TCP SYN divides by zero and panics the kernel.

Reject the bogus fingerprint in nfnl_osf_add_callback() above the
per-option for-loop. f->wss is per-fingerprint, not per-option, so
the check must run regardless of f->opt_num (including 0). Also
reject wss.wc >= OSF_WSS_MAX; nf_osf_match_one() already treats that
as "should not happen".

Crash:
 Oops: divide error: 0000 [#1] SMP KASAN NOPTI
 RIP: 0010:nf_osf_match_one (net/netfilter/nfnetlink_osf.c:98)
 Call Trace:
 <IRQ>
  nf_osf_match (net/netfilter/nfnetlink_osf.c:220)
  xt_osf_match_packet (net/netfilter/xt_osf.c:32)
  ipt_do_table (net/ipv4/netfilter/ip_tables.c:348)
  nf_hook_slow (net/netfilter/core.c:622)
  ip_local_deliver (net/ipv4/ip_input.c:265)
  ip_rcv (include/linux/skbuff.h:1162)
  __netif_receive_skb_one_core (net/core/dev.c:6181)
  process_backlog (net/core/dev.c:6642)
  __napi_poll (net/core/dev.c:7710)
  net_rx_action (net/core/dev.c:7945)
  handle_softirqs (kernel/softirq.c:622)

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384; < cb833bbc1b3c51e08652d3c86298307c07d3f2db (affected, git); ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384; < 26900306a5a2c3e4f75c643a064525526bb6e5f3 (affected, git); ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384; < 0694618cf3e9b120666e31f5f383a6e466d95a0d (affected, git); ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384; < 8def8fbd23f40e945febe913d04b731012ce0082 (affected, git); ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384; < c55940895245d8ef658ab381248a28755218d625 (affected, git); ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384; < fb965b1cfe92b28d28b5ebe3116b81dbef9f2d2f (affected, git); ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384; < 9a05e195618a6d474f2bcd5b6376d0ffc2f00366 (affected, git); ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384; < 2195574dc6d9017d32ac346987e12659f931d932 (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.31 (affected); ≥ 0; < 2.6.31 (unaffected, semver); ≥ 5.10.258; ≤ 5.10.* (unaffected, semver); ≥ 5.15.209; ≤ 5.15.* (unaffected, semver); ≥ 6.1.175; ≤ 6.1.* (unaffected, semver); ≥ 6.6.141; ≤ 6.6.* (unaffected, semver); ≥ 6.12.91; ≤ 6.12.* (unaffected, semver); ≥ 6.18.33; ≤ 6.18.* (unaffected, semver); ≥ 7.0.10; ≤ 7.0.* (unaffected, semver); ≥ 7.1; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP: ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP: ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 TM MFP - GNU/Linux subsystem: ≥ 0; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.13% as of 2026-11-06; percentile 2.85%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/cb833bbc1b3c51e08652d3c86298307c07d3f2db (CNA: Linux)

- https://git.kernel.org/stable/c/26900306a5a2c3e4f75c643a064525526bb6e5f3 (CNA: Linux)

- https://git.kernel.org/stable/c/0694618cf3e9b120666e31f5f383a6e466d95a0d (CNA: Linux)

- https://git.kernel.org/stable/c/8def8fbd23f40e945febe913d04b731012ce0082 (CNA: Linux)

- https://git.kernel.org/stable/c/c55940895245d8ef658ab381248a28755218d625 (CNA: Linux)

- https://git.kernel.org/stable/c/fb965b1cfe92b28d28b5ebe3116b81dbef9f2d2f (CNA: Linux)

- https://git.kernel.org/stable/c/9a05e195618a6d474f2bcd5b6376d0ffc2f00366 (CNA: Linux)

- https://git.kernel.org/stable/c/2195574dc6d9017d32ac346987e12659f931d932 (CNA: Linux)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-784472.html (ADP: siemens-SADP)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-45841; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-45841; retrieved 2026-11-06; source updated Not reported

Revision: ab61f554089cd829f3693f50b245129955beb4b8dc4672c86758c88bc2a25b95

Canonical: https://y2.dev/cve/CVE-2026-45841

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