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CVE-2026-53240
xfrm: iptfs: fix use-after-free on first_skb in __input_process_payload
Published 2026-06-25 (4 months ago) by the Linux kernel CNA. Subsystem net/xfrm. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-53240 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 | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
__input_process_payload() stores first_skb into xtfs->ra_newskb under drop_lock when starting partial reassembly, then unlocks and breaks out of the processing loop. The post-loop check reads xtfs->ra_newskb without the lock to decide whether first_skb is still owned: if (first_skb && first_iplen && !defer && first_skb != xtfs->ra_newskb) Between spin_unlock and this read, a concurrent CPU running iptfs_reassem_cont() (or the drop_timer hrtimer) can complete reassembly, NULL xtfs->ra_newskb, and free the skb. The check then evaluates first_skb != NULL as true, and pskb_trim/ip_summed/consume_skb operate on the freed skb — a use-after-free in skbuff_head_cache. Replace the unlocked read with a local bool that records whether first_skb was handed to the reassembly state in the current call. The flag is set after the existing spin_unlock, before the break, using the pointer equality that is stable at that point (first_skb == skb iff first_skb was stored in ra_newskb).
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_iptfs.c
- What this is
- NETWORKING [IPSEC]MAINTAINERS section matched on net/xfrm/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_XFRM|CONFIG_XFRM_IPTFS' /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 does not build this code in 2 releases. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidn
- ?
- not established - no Makefile entry for the affected file
- n
- not enabled on any flavour - this release does not build the code
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_XFRM, CONFIG_XFRM_IPTFS
- 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
- 2026-06-25 (4 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.39%, higher than 31.6% 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 |
|---|---|---|
| 6.14 | 6.18.36 | 8d9a79fbf517 |
| 6.14 | 7.0.13 | ff2ee35b6ce5 |
| 6.14 | 7.1 | eb48730bb827 |
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
- The vulnerable IPTFS parser is reached from the network receive path through xfrm4/xfrm6 ESP handling, xfrm_input, and iptfs_input on an inbound IPTFS SA. A reasonable high-impact deployment is an internet-reachable IPsec/IPTFS gateway processing remote peer traffic.
- AC:LAttack complexity, low
- The bug is a use-after-free race after first_skb is handed to reassembly, and the attacker can drive the needed fragmented/reordered IPTFS packets and concurrent continuation processing. There is no condition beyond the attacker’s control once valid IPTFS ESP traffic reaches the SA.
- PR:LPrivileges required, low
- Unauthenticated packets are rejected by XFRM/ESP state lookup, replay, and crypto verification before IPTFS parsing, so a remote attacker needs valid SA access or credentials. Locally, creating the IPTFS SA requires CAP_NET_ADMIN in a network namespace, which is reachable as low privilege via user namespaces.
- UI:NUser interaction, none
- No victim user action is required after the vulnerable SA is present; packet receipt alone triggers the path. The attacker sends crafted traffic to the configured endpoint.
- S:UScope, unchanged
- The impact is kernel memory corruption within the same host kernel security authority. This is not a VM escape, IOMMU bypass, or other cross-scope boundary.
- C:HConfidentiality impact, high
- This is a use-after-free of an sk_buff from skbuff_head_cache, and freed object reuse can expose kernel memory or support stronger disclosure primitives. Under the required guidance, UAF memory corruption warrants high confidentiality impact.
- I:HIntegrity impact, high
- The stale sk_buff is subsequently used by pskb_trim, field writes, and freeing paths, giving a plausible route to heap corruption and control-flow or data corruption. Under the required guidance, UAF memory corruption warrants high integrity impact.
- A:HAvailability impact, high
- The stale sk_buff access can corrupt kernel heap state or crash in packet processing/freeing paths. A kernel oops, panic, or repeatable crash is high availability impact.