bit7z allows compression and extraction of archive files. A flaw in versions prior to 4.0.12 permits an attacker to overwrite arbitrary files by creating a symlink that points to a target file before the archive is updated, exploiting the predictable temporary file names. This results in the compromised file being replaced with data supplied by the attacker, thereby enabling data tampering, privilege escalation, or denial of service. The weakness corresponds to CWE‑377 and CWE‑59.

The vulnerable code resides in the bit7z cross‑platform C++ library. Any application that links to bit7z and performs archive updates while running as a privileged user is susceptible. Versions earlier than 4.0.12 are impacted; the fix was introduced in release 4.0.12.

The CVSS score of 6.1 indicates moderate severity. EPSS is not available and the vulnerability is not listed in the CISA KEV catalog, suggesting no current widespread exploitation. The attack likely requires local file‑system access to place the symlink before the update process runs; if the library is used in a service with elevated privileges, a local attacker could coerce the service to perform the update and overwrite critical files. The threat level remains moderate but warrants prompt remediation.