Copier
CVE-2026-23986
HIGH
GHSA-4fqp-r85r-hxqh
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
Lifecycle Timeline
4DescriptionGitHub Advisory
Copier is a library and CLI app for rendering project templates. Prior to version 9.11.2, Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use unsafe features like custom Jinja extensions which would require passing the --UNSAFE,--trust flag. As it turns out, a safe template can currently write to arbitrary directories outside the destination path by using directory a symlink along with _preserve_symlinks: true and a generated directory structure whose rendered path is inside the symlinked directory. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc. Version 9.11.2 patches the issue.
AnalysisAI
Copier versions prior to 9.11.2 allow local attackers to write arbitrary files outside the intended project destination directory by exploiting symlink handling combined with the _preserve_symlinks feature in ostensibly safe templates. A malicious template author can craft a project template that bypasses security controls without requiring unsafe flags, enabling arbitrary file overwrites within the user's write permissions. Public exploit code exists for this vulnerability.
Technical ContextAI
Affects Copier. Copier is a library and CLI app for rendering project templates. Prior to version 9.11.2, Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use unsafe features like custom Jinja extensions which would require passing the --UNSAFE,--trust flag. As it turns out, a safe template can currently write to arbitrary directories outside the destination path by using directory a symlink along with _preserve_symlinks: true and a generated directory structu
RemediationAI
A vendor patch is available — apply it immediately.
Copier versions before 9.11.2 allow local attackers to read arbitrary files outside the template directory by exploiting
Trust-boundary bypass in Copier 9.5.0 through 9.15.1 lets an attacker-controlled template execute arbitrary commands wit
Copier CLI and library versions 9.5.0 through 9.16.0 expose a trust-prefix bypass that permits unsafe template features
Same weakness CWE-61 – UNIX Symbolic Link (Symlink) Following
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External POC / Exploit Code
Leaving vuln.today