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CVE-2026-89564
ip: orphan prefetched skbs before multicast forwarding
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem net/ipv4. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89564 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
IPv4 and IPv6 input preserve an skb->sk association installed by bpf_sk_assign() so that local delivery can use the selected socket under RCU. Both address families can also prefetch a socket in UDP early demux. In both paths (BPF and UDP early demux) a reference is not guaranteed to be held on the socket. When a multicast packet is not locally deliverable, IPv6 hands the original skb to ip6_mr_input(). IPv4's ip_mr_input() similarly keeps the original skb when local delivery is not needed. Either path can put the skb on an unresolved multicast route queue or forward it after the receive-side RCU section ends. After the prefetched socket is destroyed, a later skb free invokes sock_pfree() and dereferences the stale skb->sk. Orphan the skb before each non-local multicast forwarding path. Local delivery retains the original skb; the existing skb_clone() calls provide multicast forwarding with a socket-free clone.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/ipv4/ipmr.c
net/ipv6/ip6_input.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on net/ipv4/ip* · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_INET|CONFIG_IP_MROUTE' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switches
- CONFIG_INET, CONFIG_IP_MROUTE
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 2.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/ipv4
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.7 | 6.12.111 | e62aef7d6a5b |
| 5.7 | 6.18.50 | a8af6fbac895 |
| 5.7 | 7.2.4 | f1281d4b9908 |
| 5.7 | 7.3 | e36ce6e78fe3 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The UAF requires the attacker to attach a no-ref skb->sk (UDP early demux or bpf_sk_assign) and destroy that socket while the skb sits on the mroute unresolved queue; a remote multicast datagram does not prefetch onto non-local ip_mr_input/ip6_mr_input (mcast early demux needs membership, which clones; ip_forward drops skb->sk).
- AC:LAttack complexity, low
- The attacker owns every step: enable mroute, bind/connect a UDP socket or attach TC bpf_sk_assign, inject a non-local multicast skb so ipmr_cache_unresolved() queues it for 10s, then close the socket and wait for kfree_skb; no uncontrolled race or memory layout is required.
- PR:LPrivileges required, low
- MRT_INIT needs a raw IGMP/ICMPv6 socket (ns_capable CAP_NET_RAW) and VIFs/TC bpf_sk_assign need CAP_NET_ADMIN in the netns; an unprivileged user obtains both via unshare -Urn and never needs real init-namespace root.
- UI:NUser interaction, none
- The attacker performs the entire setup, packet injection, and socket close in their own user/net namespace; no other user must mount, open a file, or otherwise interact.
- S:UScope, unchanged
- The sock_pfree use-after-free corrupts kernel memory in the same host networking authority and does not cross a VM, IOMMU, or other security boundary.
- C:HConfidentiality impact, high
- sock_pfree() dereferences the stale skb->sk after the SOCK_RCU_FREE socket is destroyed; that UAF on a struct sock can be reclaimed with attacker-controlled objects, yielding an arbitrary read primitive.
- I:HIntegrity impact, high
- If the reused object looks refcounted, sock_pfree() calls sock_gen_put() and refcount_dec_and_test() on the freed sock, giving a UAF write/control-flow hijack primitive via heap spray.
- A:HAvailability impact, high
- Freeing the queued skb after socket destruction oopses in sock_pfree() even without a full exploit, so the bug is a reliable kernel crash as well as a UAF.