A vulnerability in the Copier library allows attackers to forge template URLs that contain percent‑encoded parent‑directory references or encoded path separators. When such URLs are entered, the URL is matched against a configured trusted repository prefix before the HTTP server or Git client performs decoding, enabling code from an untrusted repository to be executed as if it were part of the trusted set. This bypass of the trust boundary can lead to the execution of malicious template features, exposing the system to arbitrary code execution. The weakness is classified as CWE‑180 and CWE‑22, reflecting code injection via percent‑encoding and path traversal.

The affected product is Copier by copier‑org. All releases from 9.5.0 through 9.16.0 are vulnerable. Versions starting with 9.17.0 contain the fix.

The CVSS score of 7.5 indicates a high risk, but the EPSS score is below 1%, suggesting that the likelihood of exploitation in the wild is low. The vulnerability is not listed in the CISA KEV catalog. Exploitation requires an attacker to supply a crafted template URL and for the victim to run Copier against it, after which the malicious code would be executed. Users who frequently pull templates from external sources should treat this as a potential remote code execution risk.