fix: prevent following symlinks when copying files in BentoStore#5598
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Signed-off-by: Frost Ming <me@frostming.com>
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This PR contains the following updates: | Package | Type | Update | Change | OpenSSF | |---|---|---|---|---| | [bentoml](https://redirect.github.com/bentoml/bentoml) | project.dependencies | patch | `1.4.38` → `1.4.39` | [](https://securityscorecards.dev/viewer/?uri=github.com/bentoml/bentoml) | --- > [!WARNING] > Some dependencies could not be looked up. Check the [Dependency Dashboard](../issues/12) for more information. --- ### BentoML has Information Disclosure in `bentoml build` via symlink traversal in the build context [CVE-2026-40610](https://nvd.nist.gov/vuln/detail/CVE-2026-40610) / [GHSA-mcfx-4vc6-qgxv](https://redirect.github.com/advisories/GHSA-mcfx-4vc6-qgxv) <details> <summary>More information</summary> #### Details ##### Summary BentoML's `bentoml build` packaging workflow follows attacker-controlled symlinks inside the build context and copies the referenced file contents into the generated Bento artifact. If a victim builds an untrusted repository or other attacker-supplied build context, the attacker can place a symlink such as `loot.txt -> /tmp/outside-marker.txt` or a link to a more sensitive local file. When `bentoml build` runs, BentoML dereferences the symlink and packages the target file contents into the Bento. The leaked file can then propagate further through export, push, or containerization workflows. ##### Details The vulnerable code walks files under the build context and copies each matched entry into the Bento source directory: ```python for root, _, files in os.walk(ctx_path): for f in files: dir_path = os.path.relpath(root, ctx_path) path = os.path.join(dir_path, f).replace(os.sep, "/") if specs.includes(path): src_file = ctx_path.joinpath(path) dst_file = target_fs.joinpath(dest_path) shutil.copy(src_file, dst_file) ``` There is no validation that the resolved path of `src_file` remains inside `ctx_path` before `shutil.copy` dereferences the source path. As a result, a repository-controlled symlink can cross the trust boundary from `attacker-controlled repository content` to `developer/CI host filesystem` during the build process. This is a build-time path traversal / symlink traversal issue in the packaging feature, not a runtime API issue. The resulting Bento may later be exported, pushed to remote storage, or converted into a container image, which amplifies the leakage impact. ##### PoC The issue was verified in WSL against BentoML 1.4.38. The following script reproduces the vulnerability by using a harmless marker file outside the build directory. ```bash mkdir -p /tmp/bento-symlink-poc cd /tmp/bento-symlink-poc printf 'BENTOML_SYMLINK_POC_123456\n' > /tmp/outside-marker.txt cat > service.py <<'EOF' import bentoml @​bentoml.service class Demo: @​bentoml.api def ping(self, x: str) -> str: return x EOF cat > bentofile.yaml <<'EOF' service: "service:Demo" include: - "service.py" - "loot.txt" EOF ln -s /tmp/outside-marker.txt loot.txt bentoml build --output tag bentoml export demo:7pilrpjtlomelwct /tmp/poc.zip mkdir -p /tmp/poc-unzip unzip -o /tmp/poc.zip -d /tmp/poc-unzip find /tmp/poc-unzip -name loot.txt -print cat /tmp/poc-unzip/**/src/loot.txt 2>/dev/null || \ find /tmp/poc-unzip -path '*/src/loot.txt' -exec cat {} \; ``` - The script creates `/tmp/outside-marker.txt` outside the build context as a stand-in for a sensitive local file. - It creates a minimal BentoML service and explicitly includes `loot.txt` in `bentofile.yaml`. - It creates `loot.txt` as a symlink to the external marker file. <img width="1531" height="648" alt="image" src="https://github.com/user-attachments/assets/1312dcf0-74b0-4fb6-a05d-b68644470d82" /> - It runs `bentoml build`, exports the generated Bento, unzips it, and reads the packaged `src/loot.txt`. - Successful exploitation is confirmed when the packaged file contains `BENTOML_SYMLINK_POC_123456`, proving that BentoML copied the external file contents rather than keeping only the symlink. <img width="1315" height="121" alt="image" src="https://github.com/user-attachments/assets/6ed34f51-9b68-4fa9-8a42-011deb84d54e" /> <img width="1697" height="760" alt="image" src="https://github.com/user-attachments/assets/9b8a8ae5-4f06-46b4-9e4a-dee25cc5d203" /> ##### Impact An attacker who can cause a developer, release engineer, or CI system to run `bentoml build` on an attacker-controlled repository can exfiltrate local files from the build host into the Bento artifact. This can expose secrets such as cloud credentials, SSH keys, API tokens, environment files, or other sensitive local configuration. Because Bento artifacts are commonly exported, uploaded, stored, or containerized after build, the leaked file contents can spread beyond the original build machine. #### Severity - CVSS Score: 5.5 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N` #### References - [https://github.com/bentoml/BentoML/security/advisories/GHSA-mcfx-4vc6-qgxv](https://redirect.github.com/bentoml/BentoML/security/advisories/GHSA-mcfx-4vc6-qgxv) - [https://github.com/advisories/GHSA-mcfx-4vc6-qgxv](https://redirect.github.com/advisories/GHSA-mcfx-4vc6-qgxv) This data is provided by the [GitHub Advisory Database](https://redirect.github.com/advisories/GHSA-mcfx-4vc6-qgxv) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### BentoML has Information Disclosure in `bentoml build` via symlink traversal in the build context [CVE-2026-40610](https://nvd.nist.gov/vuln/detail/CVE-2026-40610) / [GHSA-mcfx-4vc6-qgxv](https://redirect.github.com/advisories/GHSA-mcfx-4vc6-qgxv) <details> <summary>More information</summary> #### Details ##### Summary BentoML's `bentoml build` packaging workflow follows attacker-controlled symlinks inside the build context and copies the referenced file contents into the generated Bento artifact. If a victim builds an untrusted repository or other attacker-supplied build context, the attacker can place a symlink such as `loot.txt -> /tmp/outside-marker.txt` or a link to a more sensitive local file. When `bentoml build` runs, BentoML dereferences the symlink and packages the target file contents into the Bento. The leaked file can then propagate further through export, push, or containerization workflows. ##### Details The vulnerable code walks files under the build context and copies each matched entry into the Bento source directory: ```python for root, _, files in os.walk(ctx_path): for f in files: dir_path = os.path.relpath(root, ctx_path) path = os.path.join(dir_path, f).replace(os.sep, "/") if specs.includes(path): src_file = ctx_path.joinpath(path) dst_file = target_fs.joinpath(dest_path) shutil.copy(src_file, dst_file) ``` There is no validation that the resolved path of `src_file` remains inside `ctx_path` before `shutil.copy` dereferences the source path. As a result, a repository-controlled symlink can cross the trust boundary from `attacker-controlled repository content` to `developer/CI host filesystem` during the build process. This is a build-time path traversal / symlink traversal issue in the packaging feature, not a runtime API issue. The resulting Bento may later be exported, pushed to remote storage, or converted into a container image, which amplifies the leakage impact. ##### PoC The issue was verified in WSL against BentoML 1.4.38. The following script reproduces the vulnerability by using a harmless marker file outside the build directory. ```bash mkdir -p /tmp/bento-symlink-poc cd /tmp/bento-symlink-poc printf 'BENTOML_SYMLINK_POC_123456\n' > /tmp/outside-marker.txt cat > service.py <<'EOF' import bentoml @​bentoml.service class Demo: @​bentoml.api def ping(self, x: str) -> str: return x EOF cat > bentofile.yaml <<'EOF' service: "service:Demo" include: - "service.py" - "loot.txt" EOF ln -s /tmp/outside-marker.txt loot.txt bentoml build --output tag bentoml export demo:7pilrpjtlomelwct /tmp/poc.zip mkdir -p /tmp/poc-unzip unzip -o /tmp/poc.zip -d /tmp/poc-unzip find /tmp/poc-unzip -name loot.txt -print cat /tmp/poc-unzip/**/src/loot.txt 2>/dev/null || \ find /tmp/poc-unzip -path '*/src/loot.txt' -exec cat {} \; ``` - The script creates `/tmp/outside-marker.txt` outside the build context as a stand-in for a sensitive local file. - It creates a minimal BentoML service and explicitly includes `loot.txt` in `bentofile.yaml`. - It creates `loot.txt` as a symlink to the external marker file. <img width="1531" height="648" alt="image" src="https://github.com/user-attachments/assets/1312dcf0-74b0-4fb6-a05d-b68644470d82" /> - It runs `bentoml build`, exports the generated Bento, unzips it, and reads the packaged `src/loot.txt`. - Successful exploitation is confirmed when the packaged file contains `BENTOML_SYMLINK_POC_123456`, proving that BentoML copied the external file contents rather than keeping only the symlink. <img width="1315" height="121" alt="image" src="https://github.com/user-attachments/assets/6ed34f51-9b68-4fa9-8a42-011deb84d54e" /> <img width="1697" height="760" alt="image" src="https://github.com/user-attachments/assets/9b8a8ae5-4f06-46b4-9e4a-dee25cc5d203" /> ##### Impact An attacker who can cause a developer, release engineer, or CI system to run `bentoml build` on an attacker-controlled repository can exfiltrate local files from the build host into the Bento artifact. This can expose secrets such as cloud credentials, SSH keys, API tokens, environment files, or other sensitive local configuration. Because Bento artifacts are commonly exported, uploaded, stored, or containerized after build, the leaked file contents can spread beyond the original build machine. #### Severity - CVSS Score: 5.5 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N` #### References - [https://github.com/bentoml/BentoML/security/advisories/GHSA-mcfx-4vc6-qgxv](https://redirect.github.com/bentoml/BentoML/security/advisories/GHSA-mcfx-4vc6-qgxv) - [https://github.com/bentoml/BentoML](https://redirect.github.com/bentoml/BentoML) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-mcfx-4vc6-qgxv) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### Release Notes <details> <summary>bentoml/bentoml (bentoml)</summary> ### [`v1.4.39`](https://redirect.github.com/bentoml/BentoML/releases/tag/v1.4.39) [Compare Source](https://redirect.github.com/bentoml/bentoml/compare/v1.4.38...v1.4.39) ##### What's Changed - ci: pre-commit autoupdate \[skip ci] by [@​pre-commit-ci](https://redirect.github.com/pre-commit-ci)\[bot] in [bentoml/BentoML#5593](https://redirect.github.com/bentoml/BentoML/pull/5593) - fix: prevent following symlinks when copying files in BentoStore by [@​frostming](https://redirect.github.com/frostming) in [bentoml/BentoML#5598](https://redirect.github.com/bentoml/BentoML/pull/5598) - fix: add sharing=locked to BuildKit cache mounts for multi-arch builds by [@​lawrence3699](https://redirect.github.com/lawrence3699) in [bentoml/BentoML#5597](https://redirect.github.com/bentoml/BentoML/pull/5597) - fix: enhance Dockerfile generation by normalizing base image lines and adding tests by [@​frostming](https://redirect.github.com/frostming) in [bentoml/BentoML#5603](https://redirect.github.com/bentoml/BentoML/pull/5603) - fix: defer prometheus\_client import in bentoml.metrics to fix histogram collection in multiprocess mode by [@​ramkrishs](https://redirect.github.com/ramkrishs) in [bentoml/BentoML#5602](https://redirect.github.com/bentoml/BentoML/pull/5602) - ci: pre-commit autoupdate \[skip ci] by [@​pre-commit-ci](https://redirect.github.com/pre-commit-ci)\[bot] in [bentoml/BentoML#5605](https://redirect.github.com/bentoml/BentoML/pull/5605) - fix: handle string input in FileSchema by encoding to UTF-8 by [@​frostming](https://redirect.github.com/frostming) in [bentoml/BentoML#5606](https://redirect.github.com/bentoml/BentoML/pull/5606) ##### New Contributors - [@​lawrence3699](https://redirect.github.com/lawrence3699) made their first contribution in [bentoml/BentoML#5597](https://redirect.github.com/bentoml/BentoML/pull/5597) - [@​ramkrishs](https://redirect.github.com/ramkrishs) made their first contribution in [bentoml/BentoML#5602](https://redirect.github.com/bentoml/BentoML/pull/5602) **Full Changelog**: <bentoml/BentoML@v1.4.38...v1.4.39> </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - "" - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Enabled. ♻ **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box --- This PR was generated by [Mend Renovate](https://mend.io/renovate/). View the [repository job log](https://developer.mend.io/github/yxtay/agentic-recommenders). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0My4xNTkuMiIsInVwZGF0ZWRJblZlciI6IjQzLjE1OS4yIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6WyJzZWN1cml0eSJdfQ==--> Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
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Signed-off-by: Frost Ming me@frostming.com
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