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CVE-2026-72137
xfrm: nat_keepalive: avoid double free on send error
Published 2026-08-15 (2 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-2026-72137 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 | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
nat_keepalive_send() frees the keepalive skb whenever the IPv4 or IPv6 send helper reports an error. That cleanup is only correct before the skb is handed to the output path. Once ip_build_and_send_pkt() or ip6_xmit() takes ownership, the networking stack may already have consumed the skb before returning an error, so freeing it again is unsafe. Handle the pre-handoff failure cases inside nat_keepalive_send_ipv4() and nat_keepalive_send_ipv6(), where the caller still owns the skb, and keep nat_keepalive_send() responsible only for family dispatch and the unsupported-family cleanup path.
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_nat_keepalive.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 with an answer below compiles the affected file into the kernels it ships. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sid, bookworm · linux-6.12y
- ?
- not established - no Makefile entry for the affected file
- y
- built into the kernel image on every flavour - only a patch removes it
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 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
- 2026-08-15 (2 months 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
- 0.71%, higher than 52.6% 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 |
|---|---|---|
| 6.11 | 6.12.101 | d0a4dc7efa82 |
| 6.11 | 6.18.40 | 5b0c4c916f20 |
| 6.11 | 7.1.5 | a8a7e6a9ff8a |
| 6.11 | 7.2 | 226f4a490d1a |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | 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
- On internet-facing IPsec VPN gateways using kernel NAT keepalive, a remote attacker can induce post-handoff outbound send failures (e.g., ENOMEM from network-driven memory pressure) when periodic keepalives are transmitted, reaching the vulnerable double-free path.
- AC:LAttack complexity, low
- After an outbound ESP-in-UDP SA has NAT keepalive configured, an attacker can reliably force send errors where the stack already consumed the skb (ip6_xmit EMSGSIZE, ip_finish_output2 neighbour/ENOMEM paths) without uncontrollable races or memory layout dependencies.
- PR:NPrivileges required, none
- Remote exploitation requires no privileges on the victim; it only needs a typical IPsec NAT-T deployment where userspace already set XFRMA_NAT_KEEPALIVE_INTERVAL. Local exploitation via user namespaces needs only CAP_NET_ADMIN (PR:L), not root in the init namespace.
- UI:NUser interaction, none
- No victim or administrator interaction is needed during exploitation; NAT keepalives are sent automatically by the kernel delayed work queue on the configured interval once the XFRM SA exists.
- S:UScope, unchanged
- Impact is kernel heap corruption and privilege escalation within the same security authority; this is not a VM escape, container breakout, or IOMMU/DMA boundary bypass.
- C:HConfidentiality impact, high
- The skb double-free corrupts the slab allocator and yields use-after-free primitives that can be leveraged for arbitrary kernel memory disclosure, not merely a bounded leak or crash-only NULL dereference.
- I:HIntegrity impact, high
- Double-free heap corruption enables attacker-controlled reallocation of freed sk_buff objects, supporting arbitrary kernel memory writes, control-flow hijacking, and local privilege escalation.
- A:HAvailability impact, high
- The double-free reliably causes slab corruption, kernel oops, or panic during keepalive send-error cleanup, providing immediate and repeatable denial of service on affected systems.