nfsd: fix use-after-free due to delegation race
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Code execution
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Partial Red Hat: 3 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-416 and the CVSS impact.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Linux | Linux | 3.17 and later | 4.4.296, 4.9.294, 4.14.259, 4.19.222, 5.4.168, 5.10.85, 5.15.8, 5.16 | Patch available | CNA |
- Linux VendorLinux Affected 3.17 and later Fixed in 4.4.296, 4.9.294, 4.14.259, 4.19.222, 5.4.168, 5.10.85, 5.15.8, 5.16 Patch available CNA
CPE configurations NVD · 5
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | before 4.4.296; 4.5 to before 4.9.294; 4.10 to before 4.14.259; 4.15 to before 4.19.222; 4.20 to before 5.4.168; 5.5 to before 5.10.85; 5.11 to before 5.15.8 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc1:*:*:*:*:*:* | 5.15 rc1 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc2:*:*:*:*:*:* | 5.15 rc2 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc3:*:*:*:*:*:* | 5.15 rc3 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc4:*:*:*:*:*:* | 5.15 rc4 | Vulnerable | Linux |
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* Versions before 4.4.296; 4.5 to before 4.9.294; 4.10 to before 4.14.259; 4.15 to before 4.19.222; 4.20 to before 5.4.168; 5.5 to before 5.10.85; 5.11 to before 5.15.8 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc1:*:*:*:*:*:* Versions 5.15 rc1 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc2:*:*:*:*:*:* Versions 5.15 rc2 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc3:*:*:*:*:*:* Versions 5.15 rc3 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc4:*:*:*:*:*:* Versions 5.15 rc4 Vulnerable ·Linux
Remediation
- Fix · CNA Linux (Linux) Fixed in 4.4.296, 4.9.294, 4.14.259, 4.19.222, 5.4.168, 5.10.85, 5.15.8, 5.16
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix planned: Will not fix |
Not affected: 2 products
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
Timeline
- 2026-10-02 Threatist record created from CVE-2021-47506
References
Patch 8
- https://git.kernel.org/stable/c/04a8d07f3d58308b92630045560799a3faa3ebce
- https://git.kernel.org/stable/c/348714018139c39533c55661a0c7c990671396b4
- https://git.kernel.org/stable/c/33645d3e22720cac1e4548f8fef57bf0649536ee
- https://git.kernel.org/stable/c/2becaa990b93cbd2928292c0b669d3abb6cf06d4
- https://git.kernel.org/stable/c/e0759696de6851d7536efddfdd2dfed4c4df1f09
- https://git.kernel.org/stable/c/eeb0711801f5e19ef654371b627682aed3b11373
- https://git.kernel.org/stable/c/148c816f10fd11df27ca6a9b3238cdd42fa72cd3
- https://git.kernel.org/stable/c/548ec0805c399c65ed66c6641be467f717833ab5
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Sources
- CVE-2021-47506 · CVE Program
- CVE-2021-47506 · NVD
- FIRST EPSS
- CVE-2021-47506 · Red Hat security data · CC BY 4.0
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