Grav Blueprint Validation Bypass Enables Arbitrary File Write

Grav before 2.0.15 contains an arbitrary file write vulnerability in the Blueprint dynamic-data bare-function validation that uses an incomplete denylist instead of a positive allowlist. Attackers with page-edit or blueprint-config access can invoke the error_log function through a data directive to append PHP payloads to web-accessible files, achieving remote code execution.

Casky was already ahead

This CVE exploits attack patterns that Casky's 322matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

CVE-2026-75827 is an arbitrary file write vulnerability in Grav CMS versions before 2.0.15 that stems from incomplete denylist-based validation in Blueprint dynamic-data bare-function processing. Attackers with page-edit or blueprint-config permissions can exploit this weakness to invoke the error_log function through data directives, writing PHP payloads to web-accessible locations and achieving remote code execution. This vulnerability matters because it chains insufficient input validation (CWE-94: Improper Control of Generation of Code) with privilege escalation—users with legitimate administrative capabilities can weaponize their access to gain code execution. Organizations running Grav with multiple editors or contributors face elevated risk, as the attack requires only mid-level access rather than full administrative control.

Casky's 322 matching skills help practitioners detect this attack pattern by correlating MITRE ATT&CK techniques TA0001 (Initial Access) and TA0043 (Reconnaissance) with behavioral indicators of Blueprint abuse. Security teams using Claude's extended reasoning capabilities would identify suspicious findings such as: unusual data directive parameters in Blueprint configurations, error_log function invocations from unexpected contexts, PHP code sequences appearing in web-accessible files, and access patterns from users with page-edit roles performing actions inconsistent with normal editorial workflows. Practitioners would see alerts flagging denylist bypass attempts and the transition from reconnaissance (probing for edit capabilities) to weaponization (injecting executable payloads), enabling rapid response before code execution occurs.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

322 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-75827.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

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