CVE-2026-31680 net: ipv6: flowlabel: defer exclusive option free until RCU teardown
A race condition in the Linux kernel IPv6 flowlabel handling allows a local attacker to trigger a use-after-free crash via concurrent access to proc files.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-31680?
CVE-2026-31680 is a high-severity use after free vulnerability in Linux kernel, published on 25 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net: ipv6: flowlabel: defer exclusive option free until RCU teardown
`ip6fl_seq_show()` walks the global flowlabel hash under the seq-file RCU read-side lock and prints `fl->opt->opt_nflen` when an option block is present.
Exclusive flowlabels currently free `fl->opt` as soon as `fl->users` drops to zero in `fl_release()`. However, the surrounding `struct ip6_flowlabel` remains visible in the global hash table until later garbage collection removes it and `fl_free_rcu()` finally tears it down.
A concurrent `/proc/net/ip6_flowlabel` reader can therefore race that early `kfree()` and dereference freed option state, triggering a crash in `ip6fl_seq_show()`.
Fix this by keeping `fl->opt` alive until `fl_free_rcu()`. That matches the lifetime already required for the enclosing flowlabel while readers can still reach it under RCU.
Weakness: CWE-416
Which versions are affected by CVE-2026-31680?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31680?
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-2026-31680 being exploited?
There is no known exploitation of CVE-2026-31680 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-84213, BELL-CVE-2026-31680, DEBIAN-CVE-2026-31680, GHSA-2xwr-gh6x-hm86, ROOT-OS-DEBIAN-11-CVE-2026-31680, ROOT-OS-DEBIAN-12-CVE-2026-31680 and 3 more.