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How CVE-2026-81525 Works
CVE-2026-81525 is a high-severity improper input validation vulnerability in the MongoDB client library for PHP. The library fails to sufficiently sanitize special elements—specifically dot (.) and NUL-byte (\0) characters—in application-supplied namespace identifiers before using them to construct the target namespace for database operations.
In MongoDB, a namespace is the combination of a database name and a collection name that uniquely identifies where data is stored. When developers pass untrusted input directly into these name components, the library does not properly escape or neutralize maliciously crafted inputs. A dot (.) in a database name, or a NUL byte in either a database or collection name, shifts the namespace split performed by the server. This allows an attacker to manipulate the structural integrity of the query by injecting unintended delimiters that alter the path resolution logic within the driver.
Unlike traditional SQL injection, which targets query clauses, this vulnerability targets the metadata layer—the location where data resides. By injecting special characters into a collection name, an attacker can redirect database operations to unintended collections, potentially traversing into other databases or overwriting critical system collections. The redirection is silent: the application continues to execute without throwing errors but operates on completely different storage locations than intended by the developer.
An authenticated low-privilege attacker can exploit this to disclose sensitive information from unintended storage locations and permit unauthorized modification of data across tenants. The vulnerability carries a CVSS v3.1 base score of 8.1 (HIGH), with HIGH confidentiality and integrity impacts. The CVSS v4.0 score is 8.6 (HIGH).
DailyCVE Form:
Platform: MongoDB PHP Library
Version: <1.21.4, 2.0.0–<2.4.1
Vulnerability: Namespace Injection (CWE-943)
Severity: HIGH (CVSS 8.1)
Date: August 27, 2026
Prediction: Patch expected September 2026
What Undercode Say:
Analytics:
- Affected Packages: composer/mongodb/mongodb (PHP Library) versions <1.21.4 and >=2.0.0, <2.4.1
- Patched Versions: 1.21.4 and 2.4.1
- Related Component: MongoDB PHP Extension also affected—patched in versions 1.21.6 and 2.4.1
- Exploit Availability: No public exploits tracked as of September 2026
- Vulnerability Type: Improper Neutralization of Special Elements in Data Query Logic
Bash Commands & Code (Detection & Validation):
Check installed version of mongo-php-library via Composer composer show mongodb/mongodb | grep versions Check for vulnerable patterns in code (grep for dynamic namespace construction) grep -rn "->selectDatabase(" . --include=".php" grep -rn "->selectCollection(" . --include=".php"// Vulnerable code example (DO NOT USE) $dbName = $<em>GET['db']; // Untrusted input $collectionName = $_GET['coll']; // Untrusted input $collection = $client->selectCollection($dbName, $collectionName); $collection->find([]); // Safe code example with validation function validateNamespace(string $name): bool { // Reject dots and NUL bytes if (strpos($name, '.') !== false || strpos($name, "\0") !== false) { return false; } // Allow only alphanumeric and underscores return preg_match('/^[a-zA-Z0-9</em>]+$/', $name) === 1; } $dbName = $_GET['db']; $collectionName = $_GET['coll']; if (!validateNamespace($dbName) || !validateNamespace($collectionName)) { throw new InvalidArgumentException('Invalid database or collection name'); } $collection = $client->selectCollection($dbName, $collectionName);
Exploit: (Educational Purposes!)
An attacker can exploit this vulnerability by injecting dot (.) or NUL (\0) characters into a database or collection name parameter. For example:
Original: /api/data?db=users&coll=profiles Malicious: /api/data?db=users.finance&coll=profiles\0salaries
In the first case, the dot in `users.finance` causes the server to interpret the database as `users` and the collection as finance, potentially accessing a different tenant’s data. In the second case, the NUL byte `\0` in the collection name `profiles\0salaries` truncates the string at the NUL character, causing the operation to target the `profiles` collection instead of the intended `salaries` collection.
This allows an attacker to silently redirect read and write operations to unauthorized databases or collections, leading to data exposure, corruption, or cross-tenant data access.
Protection:
- Upgrade to MongoDB PHP Library version 1.21.4 or 2.4.1 (and PHP Extension to 1.21.6 or 2.4.1)
- Validate all database and collection names against an allowlist of permitted characters (e.g., alphanumeric and underscore only) before passing them to any MongoDB API
- Reject any name containing dot (.) or NUL (\0) characters
- Use fixed tenant-to-namespace mappings where possible instead of constructing names dynamically from user input
- Apply authorization controls that prevent a credential from accessing unrelated tenant databases or collections
Impact:
- Confidentiality: HIGH—attacker can read sensitive data from unintended databases or collections
- Integrity: HIGH—attacker can modify or overwrite data in unauthorized locations
- Availability: NONE
- Attack Vector: NETWORK
- Privileges Required: LOW
- User Interaction: NONE
- Scope: UNCHANGED
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Sources:
Reported By: github.com
Extra Source Hub:
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