BREW-MOTO-CVE-2026-58203 (GHSA-4XGF-CPJX-PC3J)
Vulnerability from osv_homebrew – Published: 2026-08-13 17:14 – Updated: 2026-08-24 09:20 – Source websiteSummary
NestedSecretsSettingsSource reads secret values from files in a configured secrets_dir. When secrets_nested_subdir=True, a directory entry inside secrets_dir that is a symbolic link pointing outside secrets_dir is followed, so files outside the configured directory are read into settings values. The same code path bypasses the documented secrets_dir_max_size protection. An attacker or lower-privileged component able to influence entries in the configured secrets directory (for example, a writable or shared secrets mount) can turn this into an unintended local file read into settings and can defeat the advertised loading-size cap. This report does not claim network reachability by itself.
Details
NestedSecretsSettingsSource performed two passes over secrets_dir using two different, inconsistent directory-traversal implementations:
- The size check in
validate_secrets_path()usedPath.glob('**/*'), which does not descend into a symbolically-linked directory. - The loader in
load_secrets()usedglob.iglob(f'{path}/**/*', recursive=True)followed byread_text(), which does follow symlinked directories and reads through the link target.
Because the two passes disagreed on symlinks, a symlinked directory inside secrets_dir whose target lives elsewhere was invisible to the size accounting (counted as 0 bytes) while still being fully read by the loader. This produces two distinct problems:
- Out-of-tree read (CWE-22 / CWE-59). A symlinked directory (or file) inside
secrets_dirthat resolves outside it is followed, and the external file's contents are loaded into the corresponding settings field. secrets_dir_max_sizebypass (CWE-400). The size check never sees the out-of-tree content, so the documented size cap is neither respected nor able to reject the oversized external file. A related amplification exists for cyclic in-tree symlinks, whichglob.iglob(recursive=True)re-traverses, inflating the size accounting and the number of loaded secrets.
Reproduction
In a clean Linux container, with a secrets_dir containing a symlink secrets/db -> /path/outside and an outside/passwd file of 512 bytes, while secrets_dir_max_size=100:
from pydantic import BaseModel
from pydantic_settings import (
BaseSettings,
SettingsConfigDict,
NestedSecretsSettingsSource,
)
class Db(BaseModel):
passwd: str | None = None
class Settings(BaseSettings):
model_config = SettingsConfigDict(
secrets_dir='secrets',
secrets_nested_subdir=True,
secrets_dir_max_size=100, # outside/passwd is 512 bytes
)
db: Db = Db()
@classmethod
def settings_customise_sources(
cls, settings_cls, init_settings, env_settings, dotenv_settings, file_secret_settings
):
return (NestedSecretsSettingsSource(file_secret_settings),)
On affected versions, Settings().db.passwd is populated with the 512-byte out-of-tree file and no SettingsError is raised, even though the file exceeds secrets_dir_max_size.
Impact
Applications that opt into NestedSecretsSettingsSource with secrets_nested_subdir=True and load secrets from a directory whose entries can be influenced by an attacker or a lower-privileged component (for example, a writable or shared secrets mount, or a secrets directory partially populated from untrusted input) are affected. The impact is:
- Confidentiality: files outside the configured
secrets_dircan be read into settings values (local file read). - Integrity / availability of the safeguard: the advertised
secrets_dir_max_sizecap can be bypassed, and cyclic symlinks can inflate resource usage during loading.
The vulnerability requires the ability to place a symbolic link inside the configured secrets directory; it is not remotely reachable on its own. Applications that do not use NestedSecretsSettingsSource, or that point secrets_dir at a directory fully under the application's control, are not affected.
Mitigation
Upgrade to pydantic-settings 2.14.2, which:
- walks the secrets directory explicitly and only descends into directories whose resolved path stays within
secrets_dir, so symlinked directories pointing outside are never followed; - uses a single, cycle-safe iterator for both the size check and the loader, so the size accounting and the loaded set are always consistent and each real directory is visited at most once;
- skips any file whose resolved path escapes
secrets_dir, as defense in depth.
If upgrading is not immediately possible, ensure the configured secrets_dir is fully owned and controlled by the application (no writable or attacker-influenced entries), or avoid secrets_nested_subdir=True.
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "pydantic-settings",
"resource_purl": "pkg:pypi/pydantic-settings@2.15.0",
"upstream_fixed_in": "2.14.2"
},
"package": {
"ecosystem": "Homebrew",
"name": "moto",
"purl": "pkg:brew/moto"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "5.2.2_2"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/pydantic-settings@2.15.0",
"name": "pydantic-settings",
"resource": "pydantic-settings",
"strategy": "registry",
"subject_version": "2.15.0"
}
]
},
"details": "### Summary\n\n`NestedSecretsSettingsSource` reads secret values from files in a configured `secrets_dir`. When `secrets_nested_subdir=True`, a directory entry inside `secrets_dir` that is a symbolic link pointing **outside** `secrets_dir` is followed, so files outside the configured directory are read into settings values. The same code path bypasses the documented `secrets_dir_max_size` protection. An attacker or lower-privileged component able to influence entries in the configured secrets directory (for example, a writable or shared secrets mount) can turn this into an unintended local file read into settings and can defeat the advertised loading-size cap. This report does not claim network reachability by itself.\n\n### Details\n\n`NestedSecretsSettingsSource` performed two passes over `secrets_dir` using two different, inconsistent directory-traversal implementations:\n\n* The size check in `validate_secrets_path()` used `Path.glob(\u0027**/*\u0027)`, which does **not** descend into a symbolically-linked directory.\n* The loader in `load_secrets()` used `glob.iglob(f\u0027{path}/**/*\u0027, recursive=True)` followed by `read_text()`, which **does** follow symlinked directories and reads through the link target.\n\nBecause the two passes disagreed on symlinks, a symlinked directory inside `secrets_dir` whose target lives elsewhere was invisible to the size accounting (counted as 0 bytes) while still being fully read by the loader. This produces two distinct problems:\n\n1. **Out-of-tree read (CWE-22 / CWE-59).** A symlinked directory (or file) inside `secrets_dir` that resolves outside it is followed, and the external file\u0027s contents are loaded into the corresponding settings field.\n2. **`secrets_dir_max_size` bypass (CWE-400).** The size check never sees the out-of-tree content, so the documented size cap is neither respected nor able to reject the oversized external file. A related amplification exists for cyclic in-tree symlinks, which `glob.iglob(recursive=True)` re-traverses, inflating the size accounting and the number of loaded secrets.\n\n#### Reproduction\n\nIn a clean Linux container, with a `secrets_dir` containing a symlink `secrets/db -\u003e /path/outside` and an `outside/passwd` file of 512 bytes, while `secrets_dir_max_size=100`:\n\n```python\nfrom pydantic import BaseModel\nfrom pydantic_settings import (\n BaseSettings,\n SettingsConfigDict,\n NestedSecretsSettingsSource,\n)\n\n\nclass Db(BaseModel):\n passwd: str | None = None\n\n\nclass Settings(BaseSettings):\n model_config = SettingsConfigDict(\n secrets_dir=\u0027secrets\u0027,\n secrets_nested_subdir=True,\n secrets_dir_max_size=100, # outside/passwd is 512 bytes\n )\n db: Db = Db()\n\n @classmethod\n def settings_customise_sources(\n cls, settings_cls, init_settings, env_settings, dotenv_settings, file_secret_settings\n ):\n return (NestedSecretsSettingsSource(file_secret_settings),)\n```\n\nOn affected versions, `Settings().db.passwd` is populated with the 512-byte out-of-tree file and **no** `SettingsError` is raised, even though the file exceeds `secrets_dir_max_size`.\n\n### Impact\n\nApplications that opt into `NestedSecretsSettingsSource` with `secrets_nested_subdir=True` and load secrets from a directory whose entries can be influenced by an attacker or a lower-privileged component (for example, a writable or shared secrets mount, or a secrets directory partially populated from untrusted input) are affected. The impact is:\n\n* **Confidentiality:** files outside the configured `secrets_dir` can be read into settings values (local file read).\n* **Integrity / availability of the safeguard:** the advertised `secrets_dir_max_size` cap can be bypassed, and cyclic symlinks can inflate resource usage during loading.\n\nThe vulnerability requires the ability to place a symbolic link inside the configured secrets directory; it is not remotely reachable on its own. Applications that do not use `NestedSecretsSettingsSource`, or that point `secrets_dir` at a directory fully under the application\u0027s control, are not affected.\n\n### Mitigation\n\nUpgrade to **pydantic-settings 2.14.2**, which:\n\n* walks the secrets directory explicitly and only descends into directories whose resolved path stays within `secrets_dir`, so symlinked directories pointing outside are never followed;\n* uses a single, cycle-safe iterator for both the size check and the loader, so the size accounting and the loaded set are always consistent and each real directory is visited at most once;\n* skips any file whose resolved path escapes `secrets_dir`, as defense in depth.\n\nIf upgrading is not immediately possible, ensure the configured `secrets_dir` is fully owned and controlled by the application (no writable or attacker-influenced entries), or avoid `secrets_nested_subdir=True`.",
"id": "BREW-moto-CVE-2026-58203",
"modified": "2026-08-24T09:20:24Z",
"published": "2026-08-13T17:14:37Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/pydantic/pydantic-settings/security/advisories/GHSA-4xgf-cpjx-pc3j"
},
{
"type": "PACKAGE",
"url": "https://github.com/pydantic/pydantic-settings"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L",
"type": "CVSS_V3"
}
],
"summary": "pydantic-settings: NestedSecretsSettingsSource follows symlinks outside secrets_dir, enabling local file read and bypassing secrets_dir_max_size",
"upstream": [
"GHSA-4xgf-cpjx-pc3j",
"CVE-2026-58203"
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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