CVE-2026-46057: Linux Kernel Privilege Escalation Flaw

CVE-2026-46057 Overview

CVE-2026-46057 affects the Linux kernel's Landlock Linux Security Module (LSM). The flaw resides in hook_cred_transfer(), which only copies the Landlock security blob when the source credential has an associated domain. This behavior conflicts with landlock_restrict_self(), which can set LOG_SUBDOMAINS_OFF on a credential without creating a domain through the ruleset_fd=-1 path. As a result, the muting flag is not preserved across fork(), and sandboxed child processes generate unexpected audit records.

Critical Impact
Sandboxed child processes lose the LOG_SUBDOMAINS_OFF setting after fork, producing unintended Landlock audit records and breaking the documented log-muting use case.

Affected Products

Linux kernel versions implementing Landlock with the LOG_SUBDOMAINS_OFF audit-control feature
Distributions shipping kernels prior to the fix commits referenced in the upstream stable tree
Workloads relying on Landlock sandboxing with subdomain log muting before forking children

Discovery Timeline

2026-05-27 - CVE-2026-46057 published to the National Vulnerability Database (NVD)
2026-05-27 - Last updated in NVD database

Technical Details for CVE-2026-46057

Vulnerability Analysis

Landlock is an unprivileged access-control mechanism in the Linux kernel that lets processes sandbox themselves. Each task carries a Landlock security blob attached to its credentials. The blob stores the active domain and per-credential audit flags, including LOG_SUBDOMAINS_OFF, which suppresses audit records originating from nested sandboxes.

The landlock_restrict_self() syscall accepts a special ruleset_fd=-1 path. This path allows a caller to set audit flags such as LOG_SUBDOMAINS_OFF without instantiating a new domain. The credential is committed with the flag set but with a NULL domain pointer.

During fork(), the child's prepare_creds() invokes hook_cred_transfer() to copy LSM state. The Landlock implementation gates the copy on the presence of a domain in the source credential. When the domain is NULL, the audit flags are silently dropped, and the child inherits a clean Landlock blob. Sandboxes applied later in the child therefore log subdomain events that the parent explicitly muted.

Root Cause

The root cause is a conditional copy in hook_cred_transfer() that treats the Landlock blob as relevant only when a domain exists. This assumption is invalidated by the domain-less audit-flag commit path in landlock_restrict_self(). The fix removes the condition and copies the credential blob unconditionally.

Attack Vector

This issue is a correctness and audit-integrity flaw rather than a memory-safety or privilege-escalation vector. A local process that calls landlock_restrict_self() with ruleset_fd=-1 to mute subdomain logging will see its setting silently dropped in any forked child. This produces noisy audit streams, can interfere with security monitoring tooling that depends on Landlock audit semantics, and can be leveraged to obscure the expected logging policy of a sandboxed workload.

No synthetic exploitation code is provided. See the upstream commits Kernel Git Commit 1c513b8, Kernel Git Commit 2fcde49, and Kernel Git Commit 874c8f8 for the precise code change.

Detection Methods for CVE-2026-46057

Indicators of Compromise

Unexpected Landlock audit records emitted by child processes whose parent had set LOG_SUBDOMAINS_OFF
Audit volume spikes from sandboxed workloads following fork() or clone() operations
Inconsistent Landlock audit behavior between parent and child within the same process tree

Detection Strategies

Compare the running kernel version on each host against the patched stable kernels referenced in the upstream commits
Review auditd logs for AUDIT_LANDLOCK_* records originating from processes whose ancestors invoked landlock_restrict_self() with ruleset_fd=-1
Validate Landlock behavior in CI by forking a child after muting subdomain logs and asserting that no audit events are produced

Monitoring Recommendations

Forward kernel audit subsystem events to a centralized logging pipeline for correlation across process trees
Track kernel package versions across the fleet and flag hosts running pre-patch builds
Alert on sustained increases in Landlock-tagged audit volume that do not correlate with new sandbox deployments

How to Mitigate CVE-2026-46057

Immediate Actions Required

Upgrade to a Linux kernel that includes the upstream fix making the Landlock credential blob copy unconditional in hook_cred_transfer()
Inventory workloads that rely on Landlock with LOG_SUBDOMAINS_OFF and prioritize their host kernels for patching
Re-validate audit pipelines after patching to confirm that subdomain log muting is preserved across fork()

Patch Information

The upstream fix removes the domain-presence check in hook_cred_transfer() and copies the Landlock credential blob unconditionally. The relevant stable-tree commits are Kernel Git Commit 1c513b8, Kernel Git Commit 2fcde49, and Kernel Git Commit 874c8f8. Apply the kernel update shipped by your distribution that backports these commits.

Workarounds

Set LOG_SUBDOMAINS_OFF in each child after fork() rather than relying on inheritance, until the patched kernel is deployed
Filter the expected spurious Landlock audit records at the audit-collection layer to reduce noise without masking real events
Avoid the ruleset_fd=-1 audit-only configuration path on unpatched kernels when forking is required

bash

# Verify the running kernel version and confirm vendor advisory coverage
uname -r
# Example: query the distribution package manager for the installed kernel build
# Debian/Ubuntu:
dpkg -l | grep linux-image
# RHEL/Fedora:
rpm -q kernel