In the Linux kernel, fscrypt_ioctl_set_policy() performed an owner check using &nop_mnt_idmap instead of the mount’s idmap when setting an encryption policy. This caused the kernel to compare the caller’s fsuid against an unmapped on‑disk owner, which can deny a legitimate owner access and allow an unrelated caller to set the policy. Based on the description, it is inferred that an attacker who can issue the fscrypt ioctl on a filesystem with idmapping enabled could change the encryption policy on files they do not own, potentially altering confidentiality or integrity of encrypted data.

Affected systems include the Linux kernel in any distribution that uses fscrypt on filesystems supporting id‑mapped mounts such as ext4 and f2fs. No specific version range is provided, so any kernel version prior to the release of the upstream patch may be vulnerable.

The vulnerability requires local access to invoke the fscrypt ioctl on a mounted filesystem that has encryption and idmapping enabled; no publicly available exploits are known, and the CVE is not listed in the CISA KEV catalog. The CVSS score of 7.8 indicates high severity, while the EPSS score of <1% suggests a low probability of exploitation. If exploited, the flaw would allow unauthorized modification of encryption policies, potentially compromising encrypted data within the affected filesystem.