EUVD-2026-66612
GHSA-g6qf-h8rr-h574
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/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
Network-accessible OAuth endpoint needs no privileges; scope changes as attacker gains victim-account resources outside their own authority; victim must actively authenticate through the crafted link.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/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
Lifecycle Timeline
2DescriptionCVE.org
Stalwart Mail Server does not compare an OAuth redirect target against any registered destination in its default configuration. The validation routine in crates/http/src/auth/oauth/registration.rs returns success immediately when the client-authentication requirement is disabled, and that requirement is false in the shipped settings, so the supplied redirect value is neither matched against a registered client nor otherwise constrained. The value is stored with the authorization code, and the login page reads it back and sends the browser to it with the code attached. A request naming a destination the attacker controls therefore delivers a valid authorization code there once the account holder authenticates, and because the token endpoint checks only that the redirect presented at exchange matches the one recorded with the code, the same party can exchange it for access and refresh tokens and read the account's mail.
AnalysisAI
OAuth authorization code hijacking in Stalwart Mail Server through v0.16.19 enables full email account takeover when a victim authenticates via a crafted phishing link. The validation routine for OAuth redirect URIs in the default shipped configuration - where client authentication is disabled - returns success immediately without comparing the supplied redirect_uri against any registered client destination, allowing any attacker-controlled URI to receive a valid authorization code. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The vulnerability is exploitable against any Stalwart Mail Server deployment where the OAuth client authentication requirement is disabled - specifically where client_auth_required is false, which is the default in shipped settings, meaning no administrator misconfiguration is required to be exposed. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:A) confirms this is a remotely exploitable, low-complexity attack requiring no privileges but needing active user interaction - the victim must follow a crafted link and authenticate through the attacker's phishing flow. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker targeting a specific Stalwart Mail Server user constructs an OAuth authorization request URL pointing to a legitimate Stalwart instance but specifying an attacker-controlled redirect_uri parameter. The attacker delivers this link via phishing email; the target follows it, is presented with a normal-looking Stalwart login page, and authenticates successfully - upon completion, the server forwards the authorization code to the attacker's endpoint. … |
| Remediation | No specific patched version has been confirmed in available data at time of analysis; administrators should monitor the Stalwart release page at https://github.com/stalwartlabs/stalwart and issue #3205 at https://github.com/stalwartlabs/stalwart/issues/3205 for a fix release and upgrade immediately upon availability. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: disable OAuth authentication in Stalwart Mail Server or restrict access to internal networks only; audit authentication logs and mailbox access for suspicious activity. …
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