The vulnerability in Data::Intern::Shared (versions before 0.02) arises from incorrect permission assignment and insecure file opening of the mmap backing file used for shared memory segments. The file is created with mode 0666, which under default umask results in world-readable permissions (0644). Additionally, the open() call lacks O_EXCL and O_NOFOLLOW flags, allowing an attacker to pre-plant a file or symlink at the target path. This enables local attackers to read IPC payloads stored in the shared memory segment or redirect the open call to a malicious file, leading to information disclosure and potential race condition exploitation.

Local attackers with access to the shared directory (e.g., /tmp or /dev/shm) can read sensitive inter-process communication (IPC) data due to world-readable permissions on the mmap file. They can also exploit the absence of O_EXCL and O_NOFOLLOW flags to perform pre-creation race attacks or symlink attacks, potentially redirecting file operations to attacker-controlled files. The vulnerability does not impact integrity or availability but results in limited confidentiality loss.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should restrict access to shared directories where the mmap file is created and consider applying manual mitigations such as adjusting umask settings or using filesystem permissions to limit exposure. Avoid running vulnerable versions in untrusted multi-user environments.