fuse-overlayfs CVE-2026-52791

Exploitation requires all of the following: (1) the target system runs fuse-overlayfs prior to version 1.17 in a rootless container deployment; (2) the container image contains at least one SUID- or SGID-marked file in its lower overlay layer; (3) the attacker controls a low-privileged process within the container that can call open(O_TRUNC) or truncate on that file to trigger copy-up. The AT:P precondition in the CVSS 4.0 vector reflects requirement (2) - absence of SUID/SGID binaries in the lower layer fully blocks exploitation. Exploitation is further constrained to local-only access (AV:L); no network-based or unauthenticated exploitation path exists. Host-level privilege escalation is not implied by the vulnerability's described impact.

The CVSS 4.0 score of 2.0 (AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N) accurately reflects the constrained real-world risk. The AT:P metric is critical: exploitation requires a specific precondition - a SUID- or SGID-marked file must exist in the container image's lower overlay layer and be accessible to the attacker's process. Without that precondition, there is no vulnerable code path. The impact is limited to integrity of file mode bits within the container's upper layer (VI:L), with no confidentiality or availability impact and no scope change to host systems. No EPSS data was provided in the input; the absence of a KEV listing and public exploit code further depresses real-world urgency. This is not a high-priority emergency but a genuine correctness defect that should be patched in routine maintenance cycles, particularly for environments that deploy SUID/SGID binaries in rootless container images.

A low-privileged attacker with process execution inside a rootless container backed by fuse-overlayfs identifies a SUID or SGID binary in the container image's lower layer. The attacker opens the file with O_TRUNC, triggering a copy-up to the upper layer; the unpatched code preserves the SUID/SGID bits, resulting in the upper-layer file being mode 4777 (world-writable and setuid). The attacker can then write arbitrary content to that setuid file, potentially influencing other container processes that execute it. No public POC has been identified at time of analysis.