CVE-2021-47506 nfsd: fix use-after-free due to delegation race
A race condition in the Linux kernel NFS server allows attackers to trigger a use-after-free, potentially leading to code execution or system crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-47506?
CVE-2021-47506 is a critical use after free vulnerability in Linux kernel, published on 24 May 2024. 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:
nfsd: fix use-after-free due to delegation race
A delegation break could arrive as soon as we've called vfs_setlease. A delegation break runs a callback which immediately (in nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we then exit nfs4_set_delegation without hashing the delegation, it will be freed as soon as the callback is done with it, without ever being removed from del_recall_lru.
Symptoms show up later as use-after-free or list corruption warnings, usually in the laundromat thread.
I suspect aba2072f4523 "nfsd: grant read delegations to clients holding writes" made this bug easier to hit, but I looked as far back as v3.0 and it looks to me it already had the same problem. So I'm not sure where the bug was introduced; it may have been there from the beginning.
Weakness: CWE-416
Which versions are affected by CVE-2021-47506?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-47506?
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-2021-47506 being exploited?
There is no known exploitation of CVE-2021-47506 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-47506, UBUNTU-CVE-2021-47506.