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Grav: .htaccess file extension rules bypass via case variation on case-insensitive filesystems

High severity GitHub Reviewed Published Jun 29, 2026 in getgrav/grav • Updated Aug 19, 2026

Package

composer getgrav/grav (Composer)

Affected versions

< 2.0.4

Patched versions

2.0.4

Description

Summary

The default .htaccess shipped with Grav (and the reference webserver-configs/htaccess.txt) contains security rules that block direct HTTP access to sensitive file types (.yaml, .yml, .php, .json, .twig, etc.) under user/ and system/vendor/ directories. However, these rules lack the [NC] (No Case) flag, making them case-sensitive. On case-insensitive filesystems (Windows/NTFS, macOS/HFS+, or Linux with Docker volumes mounted from Windows/macOS), an attacker can bypass these rules by requesting files with uppercase extensions (e.g., .YAML, .PHP, .JSON).

Affected Versions

  • Grav 2.0.1 (latest stable as of June 2026) — confirmed
  • Grav 1.7.x — likely affected (same .htaccess rules)
  • All versions shipping the current webserver-configs/htaccess.txt

Affected Component

File: .htaccess (root of Grav installation)
Reference: webserver-configs/htaccess.txt

Affected Rules (lines 68, 70, 72)

# Line 68 — system/vendor file types
RewriteRule ^(system|vendor)/(.*)\.(txt|xml|md|html|htm|shtml|shtm|json|yaml|yml|php|php2|php3|php4|php5|phar|phtml|pl|py|cgi|twig|sh|bat)$ error [F]

# Line 70 — user file types
RewriteRule ^(user)/(.*)\.(txt|md|json|yaml|yml|php|php2|php3|php4|php5|phar|phtml|pl|py|cgi|twig|sh|bat)$ error [F]

# Line 72 — .md files globally
RewriteRule \.md$ error [F]

All three rules use [F] without [NC], making the extension match case-sensitive.

Steps to Reproduce

  1. Install Grav on a system with a case-insensitive filesystem:

    • Windows (native WAMP/XAMPP)
    • macOS (default HFS+)
    • Docker on Windows/macOS with volume mounts (e.g., ./data:/var/www/html)

  2. Create or use any plugin that stores sensitive data in its YAML config (e.g., API keys):

    user/plugins/my-plugin/my-plugin.yaml

  3. Request the file with a case-varied extension:

    GET /user/plugins/my-plugin/my-plugin.YAML HTTP/1.1

  4. Expected: HTTP 403 Forbidden

  5. Actual: HTTP 200 OK — full file contents returned, including any API keys or sensitive configuration

Impact

  • Information disclosure: Plugin configuration files (.yaml) containing API keys, credentials, or sensitive settings can be read by unauthenticated users
  • Source code exposure: PHP source files can be downloaded (instead of executed) when requested with .PHP extension on some configurations
  • Configuration exposure: user/config/system.yaml, user/config/site.yaml, and other system configuration files are accessible

Fix

Add the [NC] flag to the three affected rules:

RewriteRule ^(system|vendor)/(.*)\.(txt|xml|md|html|htm|shtml|shtm|json|yaml|yml|php|php2|php3|php4|php5|phar|phtml|pl|py|cgi|twig|sh|bat)$ error [F,NC]
RewriteRule ^(user)/(.*)\.(txt|md|json|yaml|yml|php|php2|php3|php4|php5|phar|phtml|pl|py|cgi|twig|sh|bat)$ error [F,NC]
RewriteRule \.md$ error [F,NC]

The [NC] flag makes the extension matching case-insensitive, covering .YAML, .Yaml, .PHP, .Json, etc.

Mitigating Factors

  • On native Linux with ext4 filesystem (case-sensitive), the attack does not work because Apache cannot resolve the uppercase filename to the actual file
  • Grav 2.0's Twig sandbox blocks access to plugins config subtree from page content, preventing SSTI-based config exfiltration
  • The user/accounts/, user/config/, and user/data/ folders have separate rules (line 62, 66) that block ALL file types regardless of extension — these are not affected

Environment

  • Grav: 2.0.1
  • PHP: 8.3
  • Apache: 2.4 with mod_rewrite
  • OS: Docker (php:8.3-apache) with volume mounted from Windows 10 (NTFS)
  • Tested: June 2026

Reporter

Sisnetic

References

@rhukster rhukster published to getgrav/grav Jun 29, 2026
Published by the National Vulnerability Database Aug 19, 2026
Published to the GitHub Advisory Database Aug 19, 2026
Reviewed Aug 19, 2026
Last updated Aug 19, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(33rd percentile)

Weaknesses

Improper Handling of Case Sensitivity

The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results. Learn more on MITRE.

CVE ID

CVE-2026-62673

GHSA ID

GHSA-vwg3-w8w3-pc79

Source code

Credits

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