CVE-2026-58203 in pydantic
Summary
by MITRE • 07/06/2026
pydantic-settings provides settings management using Pydantic. From 2.12.0 until 2.14.2, 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 vulnerability is fixed in 2.14.2.
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Analysis
by VulDB Data Team • 07/06/2026
The pydantic-settings library serves as a critical component for managing application configurations through Pydantic's validation mechanisms, handling sensitive data through its secrets management features. When applications utilize this library's NestedSecretsSettingsSource functionality, they expect strict containment of secret file access within a designated directory structure defined by the secrets_dir parameter. The vulnerability arises from improper handling of symbolic links within nested directory structures where the secrets_nested_subdir=True configuration option is enabled.
The technical flaw exists in how the NestedSecretsSettingsSource processes directory entries when symbolic links are present within the configured secrets directory. Specifically, when a symbolic link points outside the designated secrets_dir boundary, the code follows these links without proper validation or containment checks. This behavior violates the fundamental security principle of containment and allows unauthorized access to files located outside the intended configuration scope. The flaw is particularly dangerous because it operates through the same code path that should enforce the documented secrets_dir_max_size protection mechanism.
This vulnerability creates a significant operational impact by enabling attackers with write access to the secrets directory to perform unintended local file reads. An attacker could place a symbolic link within the configured secrets directory that points to sensitive system files such as /etc/shadow, /etc/passwd, or application configuration files containing credentials. The bypass of the advertised loading-size cap further amplifies the risk by potentially allowing large files to be loaded into settings without size restrictions, creating potential denial-of-service conditions or information disclosure scenarios.
The vulnerability aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and CWE-921 (Storage of Sensitive Data in a System File), reflecting improper path traversal and insecure file handling practices. From an ATT&CK perspective, this maps to T1566 (Phishing) and T1078 (Valid Accounts) where attackers could leverage compromised write access to secrets directories to gain information disclosure. The vulnerability also relates to T1213 (Data from Information Repositories) as it enables unauthorized data extraction from system files.
Organizations using pydantic-settings versions between 2.12.0 and 2.14.2 should immediately upgrade to version 2.14.2 or later where the fix has been implemented. The mitigation strategy involves implementing strict directory containment policies, ensuring that secrets directories are not writable by untrusted users or processes, and monitoring for symbolic link entries within configuration directories. Additionally, system administrators should review existing secrets configurations to ensure proper directory permissions and implement monitoring solutions to detect unauthorized symbolic link creation within sensitive directories. The fix in version 2.14.2 properly enforces the containment boundaries while maintaining the intended functionality of nested secret loading.