CVE-2026-71259 in ESPHome
Summary
by MITRE • 08/05/2026
ESPHome through 2026.7.0-dev contains an operator-precedence bug in the cv.url() validator in esphome/config_validation.py: `if parsed.scheme and parsed.netloc or parsed.scheme == "file": return parsed.geturl()`. Because `and` binds tighter than `or`, any file: URI passes validation regardless of netloc. This validator gates the `url:` field of the external_components YAML directive's git source schema, which is passed to `git clone` (git supports file:// natively). A crafted `external_components` block with `url: "file:///attacker/repo"` clones an attacker-controlled local path, which is then added to Python's import machinery via ESPHome's component loader, executing arbitrary Python code when the YAML configuration is processed (e.g. via `esphome config`/`esphome run`).
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Analysis
by VulDB Data Team • 08/05/2026
The vulnerability exists in ESPHome versions up to 2026.7.0-dev where a critical operator precedence bug affects the cv.url() validator located in esphome/config_validation.py. This flaw stems from the logical expression `if parsed.scheme and parsed.netloc or parsed.scheme == "file": return parsed.geturl()` which demonstrates improper handling of boolean operations due to operator precedence rules. The issue arises because the logical AND operator binds more tightly than OR, causing the validation logic to incorrectly evaluate file URI schemes regardless of whether a network location is present.
The vulnerability operates within the external_components YAML directive's git source schema where the url field is validated through this flawed function. When an attacker crafts a malicious configuration using `url: "file:///attacker/repo"`, the validator accepts the input even though it should require proper network location information for non-file schemes. This validation bypass enables arbitrary code execution through the Python import machinery since ESPHome's component loader processes the cloned repository, effectively allowing remote code execution when the YAML configuration is processed during commands like `esphome config` or `esphome run`.
The operational impact of this vulnerability aligns with CWE-691 and represents a privilege escalation vector that allows unauthenticated attackers to execute arbitrary Python code on systems running ESPHome. This weakness maps directly to ATT&CK technique T1059.001 for execution through Python, and T1021.004 for remote services exploitation. The vulnerability is particularly dangerous because it leverages legitimate Git functionality while exploiting a logic flaw in input validation, making it difficult to detect through traditional security controls.
Mitigation strategies should focus on correcting the operator precedence in the cv.url() validator by restructuring the conditional logic to properly handle the boolean operations. The fix requires modifying the validation expression to explicitly group the conditions using parentheses to ensure that file:// URIs are only accepted when they meet proper scheme and path criteria. Additionally, implementing stricter input validation for external components and restricting git clone operations to trusted sources would provide defense-in-depth protection against similar vulnerabilities in ESPHome's configuration processing pipeline.