Bug 2466993 (CVE-2026-43086)

Summary: CVE-2026-43086 kernel: Linux kernel (IPVS): Denial of Service due to NULL pointer dereference in ip_vs_add_service error path
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
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's IP Virtual Server (IPVS) component. A local attacker could trigger a NULL pointer dereference in the `ip_vs_add_service` error path. This occurs when `ip_vs_start_estimator()` fails after `ip_vs_bind_scheduler()` succeeds, leading to `ip_vs_unbind_scheduler()` being called with a NULL scheduler parameter. Successful exploitation of this vulnerability would cause a kernel panic, resulting in a Denial of Service (DoS) to the system.
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Description OSIDB Bzimport 2026-05-06 10:02:15 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ipvs: fix NULL deref in ip_vs_add_service error path

When ip_vs_bind_scheduler() succeeds in ip_vs_add_service(), the local
variable sched is set to NULL.  If ip_vs_start_estimator() subsequently
fails, the out_err cleanup calls ip_vs_unbind_scheduler(svc, sched)
with sched == NULL.  ip_vs_unbind_scheduler() passes the cur_sched NULL
check (because svc->scheduler was set by the successful bind) but then
dereferences the NULL sched parameter at sched->done_service, causing a
kernel panic at offset 0x30 from NULL.

 Oops: general protection fault, [..] [#1] PREEMPT SMP KASAN NOPTI
 KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
 RIP: 0010:ip_vs_unbind_scheduler (net/netfilter/ipvs/ip_vs_sched.c:69)
 Call Trace:
  <TASK>
  ip_vs_add_service.isra.0 (net/netfilter/ipvs/ip_vs_ctl.c:1500)
  do_ip_vs_set_ctl (net/netfilter/ipvs/ip_vs_ctl.c:2809)
  nf_setsockopt (net/netfilter/nf_sockopt.c:102)
  [..]

Fix by simply not clearing the local sched variable after a successful
bind.  ip_vs_unbind_scheduler() already detects whether a scheduler is
installed via svc->scheduler, and keeping sched non-NULL ensures the
error path passes the correct pointer to both ip_vs_unbind_scheduler()
and ip_vs_scheduler_put().

While the bug is older, the problem popups in more recent kernels (6.2),
when the new error path is taken after the ip_vs_start_estimator() call.
Comment 1 Alexander B 2026-05-06 14:51:42 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050616-CVE-2026-43086-2b1f@gregkh/T