CVE-2021-47316: linux kernel Null Dereference — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix NULL dereference in nfs3svc_encode_getaclres In error cases the dentry may be NULL. Before 20798dfe249a, the encoder also checked dentry and d_really_is_positive(dentry), but that looks like overkill to me--zero status should be enough to guarantee a positive dentry. This isn't the first time we've seen an error-case NULL dereference hidden in the initialization of a local variable in an xdr encoder. But I went back through the other recent rewrites and didn't spot any similar bugs.

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CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-476 CWE-476

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.13 — 5.13.4

References

Advisories & Patches

https://git.kernel.org/stable/c/650e6f383a6eb40f7c0a010982a74ab4b6893870 https://git.kernel.org/stable/c/ab1016d39cc052064e32f25ad18ef8767a0ee3b8 https://git.kernel.org/stable/c/e79057d15d96ef19de4de6d7e479bae3d58a2a8d https://git.kernel.org/stable/c/650e6f383a6eb40f7c0a010982a74ab4b6893870 https://git.kernel.org/stable/c/ab1016d39cc052064e32f25ad18ef8767a0ee3b8 https://git.kernel.org/stable/c/e79057d15d96ef19de4de6d7e479bae3d58a2a8d

Other References

https://cert-portal.siemens.com/productcert/html/ssa-265688.html https://cert-portal.siemens.com/productcert/html/ssa-355557.html

Frequently Asked Questions

What is CVE-2021-47316? +

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix NULL dereference in nfs3svc_encode_getaclres In error cases the dentry may be NULL. Before 20798dfe249a, the encoder also checked dentry and d_really_is_positive(dentry), but that looks like overkill to me--zero status should be enough to guarantee a positive dentry. This isn't the first time we've seen an error-case NULL dereference hidden in the initialization of a local variable in an xdr encoder. But I went back through the other recent rewrites and didn't spot any similar bugs. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2021-47316? +

CVE-2021-47316 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2021-47316? +

CVE-2021-47316 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2021-47316? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2021-47316