CVE-2023-34253: Grav vulnerable to Server-side Template Injection (SSTI) via Denylist Bypass
First published: Wed Jun 14 2023(Updated: )
Grav is a file-based Web platform. Prior to version 1.7.42, the denylist introduced in commit 9d6a2d to prevent dangerous functions from being executed via injection of malicious templates was insufficient and could be easily subverted in multiple ways -- (1) using unsafe functions that are not banned, (2) using capitalised callable names, and (3) using fully-qualified names for referencing callables. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution. A patch in version 1.7.42 improves the denylist.
Credit: security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Getgrav Grav | <1.7.42 |
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Reference Links
- https://github.com/getgrav/grav/blob/1.7.40/system/src/Grav/Common/Utils.php#L1952-L2190
- https://github.com/getgrav/grav/commit/71bbed12f950de8335006d7f91112263d8504f1b
- https://github.com/getgrav/grav/security/advisories/GHSA-j3v8-v77f-fvgm
- https://huntr.dev/bounties/3ef640e6-9e25-4ecb-8ec1-64311d63fe66/
- https://www.github.com/getgrav/grav/commit/9d6a2dba09fd4e56f5cdfb9a399caea355bfeb83
Frequently Asked Questions
What is CVE-2023-34253?
CVE-2023-34253 is a vulnerability in Grav, a file-based Web platform, where the denylist introduced in version 1.7.42 can be easily subverted, allowing the execution of dangerous functions via injection of malicious templates.
What is the severity of CVE-2023-34253?
CVE-2023-34253 has a severity level of 7.2, which is categorized as high.
How does CVE-2023-34253 affect Grav?
CVE-2023-34253 affects Grav versions up to and excluding 1.7.42. The denylist feature introduced in prior versions can be bypassed, making it possible to execute dangerous functions through injection of malicious templates.
How can I fix CVE-2023-34253 in Grav?
To fix CVE-2023-34253 in Grav, it is recommended to update to version 1.7.42 or later, which includes the necessary fixes for the vulnerability.
Where can I find more information about CVE-2023-34253?
For more information about CVE-2023-34253, you can refer to the following resources: [GitHub commit](https://github.com/getgrav/grav/commit/71bbed12f950de8335006d7f91112263d8504f1b), [Grav security advisory](https://github.com/getgrav/grav/security/advisories/GHSA-j3v8-v77f-fvgm).
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