CVE-2026-75827: Grav: Blueprint dynamic-data bare-function branch is denylist-gated and omits error_log, giving arbitrary file write

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.9%, percentile 58: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 58% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes getgrav/grav (Composer (PHP)) <= 2.0.14, fixed in 2.0.15. Check your lockfile, including transitive dependencies.

What it is

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 errorlog function through a data directive to append PHP payloads to web-accessible files, achieving remote code execution.

From the GitHub advisory

Affected versions and vulnerable location

- Confirmed on grav core at 78ebfc1 (tag 2.0.13). - Sinks: - system/src/Grav/Common/Data/Blueprint.php:455-458 calluserfuncarray($o, $params) (bare-function dynamic-data provider). - Twin: system/src/Grav/Framework/Flex/FlexDirectory.php:936-938 calluserfuncarray($function, $params). - Validation gate: Blueprint::isSafeDynamicCall() at Blueprint.php:514-536. - Class::method branch (:514-527) uses a strict positive allowlist self::$allowedDynamicCallables. - Bare-function branch (:530-534) uses only a denylist: if (isstring($function) && Utils::isDangerousFunction($function)) return false; return !self::paramsContainDangerousCallable($params);. - Denylist: Utils::isDangerousFunction() (system/src/Grav/Common/Utils.php, list around :2020-2270).

Root cause

GHSA-7pgq/CVE-2026-64850 hardened the Class::method half of the dynamic-callable validation to a positive allowlist because a page-edit account could otherwise name any static method as a provider and reach file/secret gadgets. The bare-function half was left on a denylist (isDangerousFunction). Any bare PHP function not on that list executes.

errorlog is not on the denylist (verified: no occurrence in Utils.php). errorlog($message, 3, $destination) appends attacker-controlled $message to attacker-controlled file $destination, an arbitrary-file-append primitive. paramsContainDangerousCallable() (:587-603) only scans params for dangerous callable strings, so a PHP payload string and a destination path both pass. (streamsocketclient, dl, and mbsendmail are likewise absent, giving SSRF/other primitives.)

Weakness type: CWE-94.

Product: getgrav/grav (Composer (PHP)) · Assigned by: VulnCheck · Published: 2026-08-18

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.86% probability of exploitation activity in the next 30 days; percentile 58.

Timeline

• 2026-08-18 — CVE record published by VulnCheck
• 2026-09-17 — GitHub-reviewed advisory GHSA-f8wv-xp27-6gq7 published (critical)
• 2026-10-08 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. GitHub Security Advisory (GHSA-f8wv-xp27-6gq7) github.com

Vulnerability records

1. GitHub Advisory GHSA-f8wv-xp27-6gq7 github.com
2. CVE.org record CVE-2026-75827 cve.org
3. NVD entry CVE-2026-75827 nvd.nist.gov

Other references from the CVE record and advisory

1. VulnCheck Advisory: Grav before 2.0.15 Arbitrary File Write via error_log vulncheck.com

Critical Composer (PHP) advisories · Today’s Security Digest