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Grav CMS CVE-2026-56709

| EUVDEUVD-2026-65207 HIGH
Reliance on Reverse DNS Resolution for a Security-Critical Action (CWE-350)
2026-08-25 VulnCheck GHSA-6c2c-797q-5r9x
Authentication Bypass Grav
8.7
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
8.7 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
6.8 MEDIUM

Invitation sending typically requires low-privilege CMS access (PR:L); victim must click the link (UI:R); token capture crosses into victim's authorization scope (S:C).

3.1 AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/A:N
4.0 AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Patch available
Aug 25, 2026 - 03:16 EUVD
Analysis Generated
Aug 25, 2026 - 02:21 vuln.today
CVE Published
Aug 25, 2026 - 01:30 cve.org
HIGH 8.7

DescriptionCVE.org

Grav before 3.9.2 fails to validate untrusted Host headers in the sendInvitationEmail() function when constructing token-bearing invitation links. Attackers can manipulate the Host header to poison invitation links and redirect users to attacker-controlled domains, bypassing the require_trusted_host protection which only covers password reset flows.

AnalysisAI

Host header injection in Grav CMS before 3.9.2 allows attackers to poison outgoing invitation emails, replacing the legitimate site URL with an attacker-controlled domain in token-bearing links sent via the sendInvitationEmail() function. The vulnerability exploits a gap in Grav's existing Host header defenses: the require_trusted_host protection was applied only to password reset flows, leaving invitation emails without equivalent validation. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation The user invitation feature must be in active use - the vulnerability is triggered at the moment an invitation email is dispatched from a request bearing a forged Host header. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The provided CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N) scores at 8.7, reflecting network-accessible, low-complexity exploitation with high confidentiality impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade to Grav CMS 3.9.2 or later, which applies consistent Host header validation to the sendInvitationEmail() function in line with the existing require_trusted_host protection. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Inventory all Grav CMS instances and identify those running versions before 3.9.2 with active sendInvitationEmail() usage. …

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CVE-2026-56709 vulnerability details – vuln.today
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