CVE-2026-7317: Grav CMS Deserialization RCE Vulnerability

CVE-2026-7317 Overview

A deserialization vulnerability was discovered in Grav CMS versions up to 1.7.49.5 and 2.0.0-beta.1. The vulnerability exists in the FileCache::doGet function located in system/src/Grav/Framework/Cache/Adapter/FileCache.php within the Cache Value Handler component. Successful exploitation could allow a remote attacker to execute arbitrary code through insecure deserialization of cached data, although the attack requires high complexity and is considered difficult to exploit.

Critical Impact

Remote attackers with low privileges may leverage insecure deserialization in the FileCache component to potentially inject malicious objects, leading to code execution or system compromise.

Affected Products

• Grav CMS versions up to 1.7.49.5
• Grav CMS version 2.0.0-beta.1
• Grav CMS FileCache Adapter component (system/src/Grav/Framework/Cache/Adapter/FileCache.php)

Discovery Timeline

• 2026-04-28 - CVE-2026-7317 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-7317

Vulnerability Analysis

This vulnerability stems from insecure deserialization in the Grav CMS caching mechanism. The FileCache::doGet function processes cached data without adequate validation, allowing attackers to manipulate serialized objects. When the cache retrieves and deserializes stored values, maliciously crafted serialized data could trigger object injection attacks.

The attack vector is network-based, meaning it can be exploited remotely. However, the exploitation requires authentication (low privileges) and involves high attack complexity, making successful exploitation difficult in practice. A proof-of-concept exploit has been publicly disclosed, increasing the risk profile despite the technical barriers to exploitation.

Root Cause

The root cause lies in the improper handling of deserialization within the FileCache::doGet method. The function retrieves cached values from the filesystem and deserializes them without sufficient validation of the serialized data's integrity or origin. This allows an attacker who can influence cached data to inject arbitrary serialized objects that execute malicious code upon deserialization.

The underlying issue is categorized as CWE-20 (Improper Input Validation), where the cache system fails to properly validate or sanitize input before deserializing it, creating an object injection vulnerability.

Attack Vector

The attack exploits the network-accessible cache functionality in Grav CMS. An authenticated attacker with low-level privileges could potentially poison the file cache with malicious serialized objects. When the application subsequently retrieves and deserializes this cached data through the FileCache::doGet function, the malicious payload executes.

The exploitation flow typically involves:

1. Identifying writable cache locations or cache poisoning vectors
2. Crafting a malicious serialized payload targeting available gadget chains
3. Injecting the payload into the cache storage mechanism
4. Triggering cache retrieval to execute the deserialization

For detailed technical information about this vulnerability, refer to the GitHub Security Advisory and the PoC repository.

Detection Methods for CVE-2026-7317

Indicators of Compromise

• Unusual or malformed files appearing in the Grav CMS cache directories
• Unexpected serialized data patterns in cache files containing PHP object structures
• Log entries indicating deserialization errors or object instantiation failures
• Evidence of unauthorized modifications to cache storage locations

Detection Strategies

• Monitor file system changes to the Grav CMS cache directory for suspicious serialized content
• Implement application-level logging to track cache read/write operations, particularly those involving the FileCache::doGet function
• Deploy Web Application Firewall (WAF) rules to detect and block serialized PHP object patterns in requests
• Conduct regular integrity checks on cache files to identify tampering or injection attempts

Monitoring Recommendations

• Enable verbose logging for Grav CMS cache operations to capture detailed deserialization activity
• Configure SIEM alerts for anomalous cache file modifications or access patterns
• Implement file integrity monitoring (FIM) on the system/src/Grav/Framework/Cache/Adapter/ directory
• Review web server logs for authentication anomalies from users with access to cache-related functionality

How to Mitigate CVE-2026-7317

Immediate Actions Required

• Upgrade Grav CMS to version 2.0.0-beta.2 or later, which contains the security fix
• Review cache directories for any suspicious or unauthorized serialized data
• Audit user accounts with cache-related permissions and restrict access where possible
• Apply the security patch identified as commit c66dfeb5f if unable to perform a full upgrade immediately

Patch Information

The vulnerability has been addressed in Grav CMS version 2.0.0-beta.2. The fix is identified by commit c66dfeb5f in the official Grav GitHub repository. Organizations running affected versions should upgrade to the patched version as soon as possible.

Additional details are available in the GitHub Security Advisory GHSA-gwfr-jfjf-92vv.

Workarounds

• Restrict network access to the Grav CMS administrative interface to trusted IP addresses only
• Implement additional access controls to limit which users can interact with cache functionality
• Consider disabling or restricting file-based caching temporarily while awaiting patch deployment
• Deploy a Web Application Firewall (WAF) with rules to detect and block serialized object injection attempts

# Example: Restrict cache directory permissions (adjust paths for your installation)
chmod 750 /path/to/grav/cache
chown www-data:www-data /path/to/grav/cache
# Remove potentially compromised cache data
rm -rf /path/to/grav/cache/*