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CVE-2026-92489
xfrm: Fix skb double-free in xfrm_dev_direct_output()
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem net/xfrm. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-92489 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| 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
A return value other than 1 from local_out() means that the skb has been consumed or its ownership was transferred. xfrm_dev_direct_output() nevertheless frees the skb on this path, causing a double-free when netfilter drops the packet and invalidating any other owner. Return the local_out() result directly, matching the ownership handling in xfrm_output_resume().
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/xfrm/xfrm_output.c
- What this is
- NETWORKING [IPSEC]MAINTAINERS section matched on net/xfrm/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_XFRM /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 switch
- CONFIG_XFRM
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
- 2026-09-17 (31 days ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.46%, higher than 38.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/xfrm
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.6.85 | 6.6.157 | 621871b696b1 |
| 6.12.21 | 6.12.110 | bc9297796bfd |
| 6.14 | 6.18.52 | 02deb637e965 |
| 6.14 | 7.2.6 | 56a347950e66 |
| 6.14 | 7.3 | 2aed51fc58d9 |
| 6.13.9 | 0 | 0 |
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:NAttack vector, network
- A received IPv4/IPv6 packet that ip_forward()/ip6_forward() passes through xfrm4_route_forward()/xfrm6_route_forward() reaches xfrm4_output()/xfrm6_output() then xfrm_output(); for an XFRM_DEV_OFFLOAD_PACKET tunnel SA with skb->sk NULL, that forwarded inner IP packet is what xfrm_dev_direct_output() processes.
- AC:LAttack complexity, low
- xfrm_dev_direct_output() calls nf_reset_ct() then dst->ops->local_out (__ip_local_out/__ip6_local_out), so NF_INET_LOCAL_OUT consumes the skb on DROP/QUEUE/STOLEN. The attacker owns the forwarded packet and can force that verdict (iptables/nft DROP, or nf_conntrack_in() NF_DROP when resolve_normal_ct() fails after flooding new 5-tuples); no race is required.
- PR:NPrivileges required, none
- ip_forward() and ip6_forward() take the skb with no socket or credentials; XFRM matching is only the received packet's IP selectors, not an authenticated session. CAP_NET_ADMIN is needed on the victim to install the packet-offload SA, not for the attacker who sends the inner packet.
- UI:NUser interaction, none
- The attacker triggers the bug only by sending IP packets that an already-configured packet-offload tunnel gateway forwards into xfrm_dev_direct_output(); no victim mount, open, or confirmation is required at exploit time.
- S:UScope, unchanged
- The sk_buff double-free in xfrm_dev_direct_output() corrupts kernel heap in the same kernel that performs IPsec output and is not a KVM/Xen guest-to-host escape or an IOMMU/DMA boundary bypass.
- C:HConfidentiality impact, high
- When local_out() returns != 1, nf_hook_slow() has already kfree_skb_reason()'d the skb on NF_DROP (or another owner holds it); the extra kfree_skb() in xfrm_dev_direct_output() is a sk_buff slab double-free that can be reclaimed with crafted packets to read kernel memory.
- I:HIntegrity impact, high
- The same sk_buff double-free after __ip_local_out()/__ip6_local_out() transfers ownership lets the attacker reallocate the freed object and obtain a kernel write and control-flow hijack primitive, not a crash-only integrity effect.
- A:HAvailability impact, high
- The extra kfree_skb() in xfrm_dev_direct_output() when local_out() has already consumed the skb corrupts the sk_buff cache and causes a kernel oops or panic.