Backport(v1.19) output: enforce strict path boundary validation for tag#5391
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**Which issue(s) this PR fixes**:
Fixes #
**What this PR does / why we need it**:
This PR enhances the robustness of the `${tag}` placeholder expansion by preventing unintended path boundaries from being crossed.
Previously, tags containing relative parent directory patterns (`../`) or absolute paths (e.g., `/etc/passwd`, `\Windows`) were expanded without validation in `extract_placeholders`. This could lead to unexpected file creation or access outside of the intended base directories, especially when using plugins like `out_file`.
To address this, we introduced a strict, highly optimized path boundary validation inside `extract_placeholders` specifically for the `${tag}` variable.
* By validating the variable before substitution, all core and third-party plugins using `extract_placeholders` automatically benefit from this boundary check.
* Backward Compatibility
* Tags containing safe slashes (e.g., `app/web`) are still permitted, ensuring URL expansions (e.g., in `out_http`) or safe nested directories remain fully functional.
**Docs Changes**:
**Release Note**:
Signed-off-by: Shizuo Fujita <fujita@clear-code.com>
kenhys
changed the title
kenhys
approved these changes
Jun 25, 2026
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Which issue(s) this PR fixes:
Fixes #
What this PR does / why we need it:
This PR enhances the robustness of the
${tag}placeholder expansion by preventing unintended path boundaries from being crossed.Previously, tags containing relative parent directory patterns (
../) or absolute paths (e.g.,/etc/passwd,\Windows) were expanded without validation inextract_placeholders. This could lead to unexpected file creation or access outside of the intended base directories, especially when using plugins likeout_file.To address this, we introduced a strict, highly optimized path boundary validation inside
extract_placeholdersspecifically for the${tag}variable.extract_placeholdersautomatically benefit from this boundary check.app/web) are still permitted, ensuring URL expansions (e.g., inout_http) or safe nested directories remain fully functional.Docs Changes:
Release Note: