Mattermost versions 10.10.x <= 10.10.1, 10.5.x <= 10.5.9, 10.9.x <= 10.9.4 fail to validate the redirect_to parameter, allowing an attacker to craft a malicious link that, once a user authenticates with their SAML provider, could post the user’s cookies to an attacker-controlled URL.
{
"github_reviewed": true,
"github_reviewed_at": "2025-09-16T19:54:54Z",
"cwe_ids": [
"CWE-601"
],
"severity": "HIGH",
"nvd_published_at": "2025-09-15T11:15:34Z"
}