CVE-2021-47218 selinux: fix NULL-pointer dereference when hashtab allocation fails

What is CVE-2021-47218?

CVE-2021-47218 is a medium-severity vulnerability in Linux kernel, published on 10 Apr 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

selinux: fix NULL-pointer dereference when hashtab allocation fails

When the hash table slot array allocation fails in hashtab_init(), h->size is left initialized with a non-zero value, but the h->htable pointer is NULL. This may then cause a NULL pointer dereference, since the policydb code relies on the assumption that even after a failed hashtab_init(), hashtab_map() and hashtab_destroy() can be safely called on it. Yet, these detect an empty hashtab only by looking at the size.

Fix this by making sure that hashtab_init() always leaves behind a valid empty hashtab when the allocation fails.

Weakness: CWE-476

Which versions are affected by CVE-2021-47218?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2021-47218?

Apply the vendor's patch.

Is CVE-2021-47218 being exploited?

There is no known exploitation of CVE-2021-47218 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-47218, GHSA-h6wr-63v9-2m6h, UBUNTU-CVE-2021-47218.