CVE-2021-47259 remediation guide

Linux Linux, linux_kernel, linux kernel

In the Linux kernel, the following vulnerability has been resolved: NFS: Fix use-after-free in nfs4_init_client() KASAN reports a use-after-free when attempting to mount two different exports through two different NICs that belong to the same server. Olga was able to hit this with kernels starting somewhere between 5.7 and 5.10, but I traced the patch that introduced the clear_bit() call to 4.13. So something must have changed in the refcounting of the clp pointer to make this call to nfs_put_client() the very last one.

Open CVE record

ProductLinux Linux, linux_kernel, linux kernel

Affected versions>= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < c7eab9e2d7b4e983ce280276fb920af649955897, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < 42c10b0db064e45f5c5ae7019bbf2168ffab766c, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < 3e3c7ebbfac152d08be75c92802a64a1f6471a15, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < c3b6cf64dfe4ef96e7341508d50d6998da7062c7, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < 72651c6579a25317a90536181d311c663d0329ab, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < 476bdb04c501fc64bf3b8464ffddefc8dbe01577, >= 4.13, >= 8dcbec6d20eb < 476bdb04c501, >= 4.13 < 4.14.237, >= 4.15 < 4.19.195, >= 4.20 < 5.4.126, >= 5.5 < 5.10.44, >= 5.11 < 5.12.11, 5.13

Fixed versions4.14.237, 4.19.195, 5.4.126, 5.10.44, 5.12.11

Priority basisReview · CVSS 7.8 · EPSS 0.71%

Identify the affected asset

Confirm whether Linux Linux, linux_kernel, linux kernel is installed, record the deployed version and installation path, and identify exposed interfaces.

Record the product name, package or appliance identifier, and installed version.
Identify internet-facing, administrative, API, and internal access paths.
Preserve the pre-change configuration and relevant service logs.

Validate the affected-version match

Compare the deployed version with the affected range: >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < c7eab9e2d7b4e983ce280276fb920af649955897, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < 42c10b0db064e45f5c5ae7019bbf2168ffab766c, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < 3e3c7ebbfac152d08be75c92802a64a1f6471a15, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < c3b6cf64dfe4ef96e7341508d50d6998da7062c7, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < 72651c6579a25317a90536181d311c663d0329ab, >= 8dcbec6d20eb881ba368d0aebc3a8a678aebb1da < 476bdb04c501fc64bf3b8464ffddefc8dbe01577, >= 4.13, >= 8dcbec6d20eb < 476bdb04c501, >= 4.13 < 4.14.237, >= 4.15 < 4.19.195, >= 4.20 < 5.4.126, >= 5.5 < 5.10.44, >= 5.11 < 5.12.11, 5.13. Treat incomplete inventory results as unresolved.

Prioritize with independent signals

The CVSS severity warrants an early asset and exposure review. Combine this signal with asset criticality, exposure, compensating controls, and business impact.

Apply supported remediation

Follow the vendor advisory or supported update path. Current fixed-version status: 4.14.237, 4.19.195, 5.4.126, 5.10.44, 5.12.11. Preserve configuration and rollback material before change.

Verify the result

Confirm the resulting version, service health, authentication and access paths, monitoring coverage, and relevant security logs.

Confirm the expected version and package state.
Run a functional health check for critical service paths.
Review authentication, error, application, and security monitoring logs.
Reassess exposure if the supported fix cannot be applied.

Operational boundary

This page does not replace the vendor advisory, support contract, change-management process, or recovery plan. Do not infer that an asset is unaffected from an incomplete inventory query or a missing fixed-version field.