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CVE-2026-74864 – Authentication Bypass / Privilege Escalation – SOGo (YunoHost sogo_ynh package) bef

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Summary

CVE-2026-74864 is a critical authentication bypass vulnerability affecting the sogo_yhn package, which configures the SOGo groupware/webmail suite on YunoHost. The package configures SOGo to trust the x-webobjects-remote-user HTTP header as proof of a password-validated identity, but the bundled Nginx configuration does not strip this header from incoming client requests. As a result, an unauthenticated remote attacker can supply this header directly and assume the identity of any user, including administrators, without a password. The vulnerability carries a CVSS score of 9.3 (Critical).

Technical details

  • Root cause: sogo_yhn configures SOGo with a parameter that treats requests carrying the x-webobjects-remote-user HTTP header as already-authenticated, skipping password validation.
  • Trigger condition: The front-end Nginx configuration shipped with the package does not strip or overwrite this header on inbound client requests, so a client-supplied value is passed through to SOGo unmodified.
  • Attack vector: Network — an attacker sends an HTTP request directly to the exposed SOGo instance with an arbitrary x-webobjects-remote-user header value set to a target username.
  • Impact: Full authentication bypass allowing impersonation of any existing SOGo user, including privileged/administrative accounts, with no credentials, user interaction, or special privileges required. This can lead to exposure and manipulation of mail, calendars, contacts, and other groupware data (high impact to confidentiality, integrity, and availability).
  • Classification: CWE-639 (Authorization Bypass Through User-Controlled Key).
  • Related issue: A companion vulnerability, CVE-2026-74865, was disclosed alongside this one, involving the SOGoTrustProxyAuthentication parameter bypassing HTTP Basic authentication password checks.

Affected software

  • YunoHost-Apps sogo_yhn package: all versions prior to 5.8.0~ynh9

Severity

  • CVSS Score: 9.3 (Critical)
  • CVSS v4.0 Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade the sogo_yhn package to version 5.8.0~ynh9 or later. Note that this fixed version requires YunoHost >= 12.1.38 and cannot be backported to YunoHost 11.
  • If no patch available / upgrade not yet possible: The SOGo single sign-on (SSO) feature was disabled as a temporary vendor-side workaround pending migration to SOGo 6. Administrators unable to upgrade immediately should ensure the SOGo instance is not reachable from untrusted networks, verify that no proxy or load balancer in front of the service allows client-supplied x-webobjects-remote-user headers to pass through, and review authentication logs for anomalous logins using this header.

References

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