CVE-2021-47506
A critical bug in the Linux kernel’s NFS server caused a use‑after‑free error that could corrupt memory or crash the system. The flaw occurs when a delegation break is processed after a lease is set, leading to a freed object still being referenced. The kernel has fixed the issue, but affected systems should update to a patched kernel.
An official fix is available, so this entry is kept for 30 days and then removed automatically.
Who is affected
Linux kernel 5.15 and earlier versions that have not applied the NFS delegation fix. Typical users are system administrators running NFS servers on Linux.
Real-world impact
An attacker could trigger a crash or memory corruption that might allow them to execute arbitrary code or cause denial of service on the affected system.
Why this severity
The CVSS score of 9.8 reflects that the vulnerability is exploitable from the network, requires no privileges, and can lead to complete compromise of confidentiality, integrity, and availability.
What to do about it
- 01Upgrade to a Linux kernel version that includes the NFS delegation fix.
NVD description indicates the vulnerability has been resolved.
Timeline
- May 24, 2024 · May 24, 2024PublishedDisclosed and added to the National Vulnerability Database.
- Aug 4, 2026 · 2d agoAdvisory updatedThe NVD record was last revised.
- Aug 5, 2026 · 1d agoOfficial fix availableA vendor patch or mitigation now exists — see the remediation steps above.
How it’s attacked
References & advisories
- git.kernel.org/stable/c/04a8d07f3d58308b92…patch
- git.kernel.org/stable/c/148c816f10fd11df27…patch
- git.kernel.org/stable/c/2becaa990b93cbd292…patch
- git.kernel.org/stable/c/33645d3e22720cac1e…patch
- git.kernel.org/stable/c/348714018139c39533…patch
- git.kernel.org/stable/c/548ec0805c399c65ed…patch
- git.kernel.org/stable/c/e0759696de6851d753…patch
- git.kernel.org/stable/c/eeb0711801f5e19ef6…patch