CVE-2026-88921

MISP in versions up to and including 2.5.45 does not consistently enforce the acting user's authorization when instantiating event templates. The instantiation path passed a template-specified sharing_group_id into event creation without verifying the user could use that sharing group, attached template-specified tags without checking tagging permissions, and hardcoded local => 0, allowing local_only tags to be attached globally and propagate through synchronization or export.

A vulnerability in MISP allows an authenticated user with permission to create or modify event templates to bypass validation of the template definition field. By supplying a pre-encoded string instead of an array structure, an invalid definition can be persistently stored. On retrieval, invalid JSON triggers an exception, causing HTTP 500 errors in event template functionality.

MISP contains a session fixation vulnerability in the CustomAuth authentication flow. After successful authentication via CustomAuth, MISP stores the authenticated user identity in the existing session without first rotating the session identifier. An attacker who knows the victim's session identifier before authentication can later reuse it to access the victim's authenticated session.

A vulnerability in MISP's email-based one-time password (OTP) authentication flow allowed an attacker to perform an unrestricted number of OTP verification attempts. The email_otp() endpoint did not apply brute-force protection, enabling repeated guessing of OTP and potential bypass of the additional authentication factor.

An improper authorization check in MISP's attribute creation endpoint allowed an authenticated user with permission to add attributes to submit a sharing_group_id without triggering the corresponding sharing group authorization check, as long as the attribute distribution value was not explicitly set to 4 — 'sharing group'.

In MISP versions before 2.4.80, when configured with X.509 certificate authentication alongside a non-MISP external user management API, an unauthenticated user can gain access as an arbitrary user if the API returns an empty value.

Affected versions of MISP contain insufficient validation of server-side outbound HTTP destinations in feed retrieval and TAXII discovery functionality. In feed processing, redirects were followed without validating the redirect scheme or destination, and original request headers were reused, potentially forwarding authentication headers or API credentials to a different host. Redirects could also target internal network resources, resulting in SSRF. The fix adds redirect validation, blocks internal destinations for cross-host redirects, strips configured feed credentials before following redirects to another host, and pins validated DNS results. The TAXII discovery endpoint had a related incomplete SSRF defense using gethostbyname() and comparing against only a few literal addresses, missing cases like IPv6 loopback (::1), numeric host encodings such as 0x7f000001, and multiple DNS records. The fix moves TAXII discovery to the shared URL egress validator.

MISP contains an improper TLS certificate validation vulnerability in CurlClient. The CurlClient::$verifyPeer property was not explicitly initialized and therefore defaulted to null, which when passed to cURL effectively disabled TLS peer verification unless the calling code explicitly enabled it. As a result, HTTPS connections made through affected CurlClient instances could accept certificates that were not issued by a trusted certificate authority.

MISP contains an authentication bypass vulnerability in its LDAP and LinOTP authentication components due to insufficient validation of user-supplied credentials. An attacker knowing a valid directory user's email address could submit an empty password, which may be accepted by an LDAP server allowing unauthenticated binds. Additionally, in the LinOTP component, empty passwords could be checked against local MISP password hashes, and LDAP-provisioned accounts could be created with empty local passwords.

MISP has a mass assignment vulnerability in the user edit functionality (UsersController::edit()). An authenticated attacker can modify the user ID in the request, leading to updates on another user's account.