CVE-2026-72137 xfrm: nat_keepalive: avoid double free on send error
A double free vulnerability in the Linux kernel's xfrm nat_keepalive module allows attackers to cause a denial of service or potentially execute code.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72137?
CVE-2026-72137 is a critical use after free vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
xfrm: nat_keepalive: avoid double free on send error
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.
Which versions are affected by CVE-2026-72137?
How do I fix CVE-2026-72137?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-72137 being exploited?
There is no known exploitation of CVE-2026-72137 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72137, DEBIAN-CVE-2026-72137, GHSA-w74p-mj9r-98xw, UBUNTU-CVE-2026-72137.