CVE-2026-89766
Low risk· EPSS 8%Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
In the Linux kernel, the PIDFD_GET_*_NAMESPACE ioctls in pidfd_ioctl() perform a ptrace access check based on credentials but, unlike the corresponding procfs paths, do not hold the target task's exec_update_lock. This allows a caller to pass the check against the target's old credentials and then read the namespace after the target has execve()'d a setuid binary and committed new credentials. The fix holds exec_update_lock for reading around the ptrace check and namespace lookup.
Risk Assessment
A local attacker can access namespace information they should have been denied, potentially facilitating further privilege escalation or bypassing access controls. In multi-tenant and container environments this poses a real risk to isolation.
Recommendation
Update the Linux kernel to a version containing the fix (commit described in the advisory). If updating is not possible, restrict the ability of unprivileged users to perform pidfd operations.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: pidfd: hold exec_update_lock around namespace ioctl The PIDFD_GET_*_NAMESPACE ioctls in pidfd_ioctl() perform a filesystem credentials ptrace access check before handing out a namespace file descriptor. The accompanying comment states that the code "mirrors nsfs behavior", but, unlike the corresponding procfs paths, it does so without holding the target task's exec_update_lock. proc_ns_get_link() and proc_ns_readlink() both take exec_update_lock for reading around the ptrace check and the namespace lookup, so that the credentials used for the access decision match those of the task when its namespace is read. Without it, a caller can pass the check against the target's old credentials and then read the namespace after the target has execve()'d a setuid binary and committed new credentials -- accessing namespace information it should have been denied. Hold exec_update_lock for reading around the ptrace check and the namespace lookup so that pidfd truly mirrors nsfs behavior, as the comment already claims. open_namespace() itself runs outside the lock: once a namespace reference is obtained it carries its own refcount and is opened with the caller's own credentials, so a concurrent execve() on the target can no longer affect the outcome.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS