Bug 2481867 (CVE-2026-45841)

Summary: CVE-2026-45841 kernel: netfilter: nfnetlink_osf: fix divide-by-zero in OSF_WSS_MODULO
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's netfilter component. A local attacker with CAP_NET_ADMIN capabilities, which grants certain network administration privileges, could trigger a divide-by-zero error by adding a specially crafted fingerprint via nfnetlink. This vulnerability could lead to a kernel panic, effectively causing a Denial of Service (DoS) on the affected system.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-05-27 11:01:35 UTC 
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)
Comment 1 Keith Grant 2026-05-27 12:27:52 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026052712-CVE-2026-45841-9575@gregkh/T