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CVE-2021-47316: nfsd: fix NULL dereference in nfs3svc_encode_getaclres

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-05-21 · updated 2026-10-14
• Weakness: CWE-476

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.

Affected products

• Linux kernel: from 5.13 before 5.13.4 — fixed in 5.13.4

How to fix

Upgrade to a fixed version: Linux kernel 5.13.4. Check the vendor advisory for mitigations.

References

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

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