ANALYSIS · f0ca1cfa· FINISHED 2026-06-13 · PATCHDIFF

fluentform6.1.1 → 6.1.2✓ COMPLETED

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CVE-2025-9260

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app/Services/Form/FormValidationService.php

AI: 2 vulnerabilities

CWE-502: Deserialization of Untrusted DataCWE-319: Cleartext Transmission of Sensitive InformationCWE-755: Improper Handling of Exceptional Conditions CVE-2025-9260

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CVE-2025-9260

Security writeup for CVE-2025-9260

✓ 1 FILE

## The Exploit

An authenticated attacker with Subscriber-level access or above can inject a malicious serialized PHP object via the `parseUserProperties` function in FormValidationService.php, exploiting the insecure `unserialize()` call on data from an external geolocation API.

```http
POST /wp-admin/admin-ajax.php HTTP/1.1
Host: target-site.local
Content-Type: application/x-www-form-urlencoded
Cookie: wordpress_logged_in=subscriber_session_token

action=fluentform_get_country_code&ip=127.0.0.1
```

The attacker intercepts the HTTP request to `http://www.geoplugin.net/php.gp?ip=<IP>` (vulnerable code makes unencrypted calls) or compromises the endpoint, replacing the expected serialized PHP object with a malicious payload. When the response reaches `unserialize($body)` at line 723, the PHP engine instantiates arbitrary objects. If a POP (Property-Oriented Programming) chain exists in loaded WordPress plugins or the application itself, the attacker chains `__construct()`, `__destruct()`, or `__get()` magic methods to read files via LFI or achieve RCE if `allow_url_include` is enabled.

Observable outcome: the attacker reads `/etc/passwd` or other sensitive files; in RCE scenarios, arbitrary PHP code executes in the web server's context.

---

## What the Patch Did

**Before:**

```php
$request = wp_remote_get("http://www.geoplugin.net/php.gp?ip={$ip}");

// ... response validation ...

$body = unserialize($body);
```

**After:**

```php
$request = wp_remote_get("https://apip.cc/api-json/{$ip}");

// ... response validation ...

$body = \json_decode($body, true);
```

The patch replaced PHP's `unserialize()` function with `json_decode()`, which parses JSON safely without instantiating arbitrary objects. Additionally, the endpoint URL was changed from unencrypted HTTP to HTTPS and the API provider was swapped, reducing both the deserialization attack surface and the risk of MITM interception of geolocation data. The core control is the substitution of **unsafe deserialization** (`unserialize()`) with **type-safe JSON parsing** (`json_decode(..., true)`), which only produces primitive PHP arrays and scalars, never object instances.

---

## Root Cause

**CWE-502: Deserialization of Untrusted Data.**

The `$body` variable is extracted from the HTTP response body returned by `wp_remote_get()` via `wp_remote_retrieve_body($request)`. This response originates from an external API endpoint over which the application has no cryptographic control (HTTP, not HTTPS in the original code). The attacker either compromises the remote endpoint or performs a man-in-the-middle attack on the unencrypted channel. The untrusted `$body` is passed directly to `unserialize()` at line 723 without any validation, deserialization filter, or allowlist. The dataflow is: attacker-controlled HTTP response body → `$body` variable → `unserialize()` sink. PHP's object deserialization engine respects the serialized class names and properties, allowing instantiation of any class in scope, which then triggers magic methods during object construction or destruction.

---

## Why It Works

The **single load-bearing line** is the replacement of `unserialize($body)` with `json_decode($body, true)`. Without this change, an attacker can still inject serialized objects. The second argument `true` to `json_decode()` is critical: it forces the return type to be a PHP array, never an object, which neutralizes all POP chain attacks because magic methods are never invoked. The engineer also upgraded from HTTP to HTTPS and changed the API provider as defence-in-depth, reducing the likelihood of successful MITM interception and shrinking the trusted endpoint surface. However, these changes are supplementary; the core protection is the elimination of object deserialization. If the HTTPS and provider-swap changes were reverted but `unserialize()` remained replaced with `json_decode()`, the vulnerability would remain closed. Conversely, if only the endpoint URL was changed without replacing `unserialize()`, an attacker could still exploit it via POP chains if they compromise the new API or find another way to influence the response.

---

## Hardening Checklist

- **Never call `unserialize()` on data from external sources, user input, or untrusted caches.** Use `json_decode()` for JSON, or implement a strict schema validator (e.g., JSON Schema validation via `wp_json_validate_object()` or a library like `league/json-guard`) if structured data is required.

- **Always use HTTPS for all outbound HTTP requests,** especially those that fetch data for deserialization or caching. In WordPress, wrap `wp_remote_get()` calls with `https://` URLs and test with `wp_safe_remote_get()` if available.

- **Implement response validation before deserialization.** Check HTTP status codes (`wp_remote_retrieve_response_code()`) and validate the response body structure (e.g., presence of expected keys) before parsing, using helpers like `Arr::get()` with sensible defaults.

- **Audit all uses of `unserialize()` in your plugin codebase via grep and PHPStan.** Replace with `json_decode()` or custom parsing functions that only extract primitive types.

- **Add integration tests that mock external API responses with malicious payloads** (e.g., serialized objects or code injection attempts) and verify that the application does not instantiate objects or execute arbitrary code.

---

## References

- https://nvd.nist.gov/vuln/detail/CVE-2025-9260

CVE CVE-2025-9260

PRODUCT fluentform

AFFECTED ≤ 6.1.1

FIXED IN 6.1.2

STATUS Generated

Security writeup · CVE-2025-9260

Source files · 1

app/Services/Form/FormValidationService.php Linked

↗ NVD