CVE-2026-33550: 
NixOS vulnerability analysis and mitigation

CVE-2026-33550 is an OTP (One-Time Password) implementation flaw in SOGo, the open-source groupware server developed by Alinto. The vulnerability affects all SOGo versions before 5.12.5 and stems from two related weaknesses: the TOTP secret is not renewed when a user disables and re-enables the OTP feature, and the OTP key length is only 12 digits instead of the recommended 20, reducing entropy. It was published on March 22, 2026, and carries a CVSS v3.1 base score of 2.6 (Low) (Feedly, SOGo Release).

The root cause is classified as CWE-308 (Use of Single-factor Authentication), reflecting insufficient OTP secret management. Prior to version 5.12.5, SOGo derived the TOTP key from the first 12 characters of the user's private salt (userPrivateSalt substringToIndex: 12) and never regenerated this key when a user toggled the OTP feature off and back on. The fix introduces a dedicated totpKey parameter stored in user settings, generated as a 20-character SHA1-derived string, and a renew flag that forces key regeneration when TOTP is disabled and re-enabled. Backward compatibility is maintained by falling back to the old key derivation method during login for pre-5.12.5 configurations (GitHub Commit).

Successful exploitation could allow an attacker with prior knowledge of or access to the user's private salt to predict or brute-force the TOTP code, potentially bypassing multi-factor authentication. The reduced key space (12 digits vs. the recommended 20) significantly lowers the computational effort required for brute-force attacks. The integrity impact is limited — an attacker could gain unauthorized access to a user's SOGo account — but confidentiality and availability are not directly affected according to the CVSS assessment (Feedly).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation as of the time of disclosure (Feedly). The EPSS score is approximately 0.024%, indicating a very low probability of exploitation in the near term. Exploitation requires the attacker to have elevated privileges and user interaction, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The attack complexity is rated High, as the attacker would need access to the user's salt or the ability to brute-force the shortened key space within the TOTP time window (Feedly).

1. Reconnaissance: Identify a target SOGo instance running a version prior to 5.12.5 with TOTP/MFA enabled for user accounts.
2. Obtain private salt: Gain access to the user's userPrivateSalt value — this may require database access, a separate vulnerability, or insider knowledge, as the salt is stored in SOGo's user settings.
3. Derive the TOTP key: Extract the first 12 characters of the private salt (substringToIndex: 12), which was used as the TOTP secret in vulnerable versions.
4. Generate valid TOTP codes: Use a standard TOTP library (e.g., oathtool) with the derived 12-character secret to generate valid time-based codes: oathtool --totp --base32 <base32-encoded-12-char-salt>.
5. Bypass MFA: Submit the generated TOTP code alongside valid credentials to authenticate to the SOGo web interface, bypassing the MFA control (GitHub Commit).

Upgrade SOGo to version 5.12.5 or later, which introduces proper TOTP key renewal on disable/re-enable and increases the key length to 20 characters. The patch is available via the official Alinto GitHub repository (SOGo Release, GitHub Commit). For organizations unable to patch immediately, restrict network-level access to the SOGo interface, enforce strong primary passwords, and monitor authentication logs for anomalous TOTP validation attempts. Note that version 5.12.5 maintains backward compatibility with existing TOTP configurations, migrating old secrets to the new storage format transparently on first login.

The vulnerability was noted in automated vulnerability tracking feeds and security databases shortly after disclosure, with coverage on platforms including Bluesky and various CVE aggregation services (Feedly). The Alinto team acknowledged the issue in the SOGo 5.12.5 release notes, crediting the community for finding and reporting it, and included the fix alongside several other security patches in the same release (SOGo Release). No significant broader media coverage or notable researcher commentary beyond standard vulnerability tracking has been observed.