CVE-2025-53603: 
SOGo vulnerability analysis and mitigation

CVE-2025-53603 is a NULL pointer dereference vulnerability in Alinto SOPE, the Objective-C framework powering the SOGo groupware server. It affects SOPE/SOGo versions 2.0.2 through 5.12.2 and allows an unauthenticated remote attacker to crash the SOGo process by sending a crafted HTTP request. The vulnerability was discovered and disclosed by Stefan Bühler on July 2, 2025, via the oss-security mailing list, with CVE assignment confirmed on July 5, 2025. It carries a CVSS v3.1 base score of 7.5 (High) (oss-security, Red Hat CVE).

The root cause (CWE-476: NULL Pointer Dereference) lies in sope-core/NGExtensions/NGHashMap.m at line 790, where the expression root->last->next = element; is executed without checking whether root->last is NULL. The last pointer is only maintained by -[NGMutableHashMap addObjects:count:forKey:]; when an NGHashMap is cloned (e.g., during request parsing), the copied nodes have last == NULL. SOPE's request handling first parses the POST body into an NGHashMap for form parameters, clones it, and then merges query string parameters into the clone — if a parameter key appears in both the POST body and the query string, the duplicate key triggers the NULL dereference and causes a segfault. The bug has existed since commit dfceefc on 2012-10-15 and is trivially exploitable with a single curl command: curl -d 'x=' 'https://.../SOGo/?x=' (oss-security, GitHub PR #69).

Successful exploitation causes an immediate crash (segfault) of the SOGo process, resulting in a complete denial of service for all users of the affected groupware instance. The impact is limited to availability — there is no confidentiality or integrity impact, as the vulnerability does not enable code execution or data access. Any unauthenticated attacker with network access to the SOGo endpoint can repeatedly trigger the crash, effectively keeping the service unavailable (oss-security, Red Hat CVE).

The vulnerability is trivially exploitable with no authentication required and minimal technical skill — a single curl command is sufficient to crash the server. No exploit kit or weaponized tooling has been publicly reported, but the simplicity of the trigger effectively makes any public disclosure a functional PoC. The EPSS score is approximately 0.042%, indicating low predicted exploitation probability in the near term. There is no evidence of in-the-wild exploitation or CISA KEV catalog listing as of the time of this report (oss-security, Feedly).

1. Reconnaissance: Identify internet-facing SOGo instances (versions 2.0.2–5.12.2) using tools like Shodan or Censys by searching for SOGo login pages or HTTP headers characteristic of SOGo deployments.
2. Craft the malicious request: Prepare an HTTP POST request where at least one query string parameter name is identical to a parameter name in the POST body (e.g., parameter x appears in both).
3. Send the request: Execute the request against any SOGo endpoint, for example: curl -d 'x=' 'https://<target>/SOGo/?x='
4. Trigger the crash: SOPE parses the POST body into an NGHashMap, clones it (setting last = NULL on all nodes), then attempts to merge the duplicate query string parameter — dereferencing the NULL last pointer at NGHashMap.m:790, causing a segfault and SOGo process crash.
5. Sustain DoS: Repeat the request as needed to prevent service recovery if the process is automatically restarted (oss-security, GitHub PR #69).

• Network: HTTP POST requests to any SOGo endpoint (e.g., /SOGo/, /SOGo/so/) where the same parameter name appears in both the query string and the POST body (e.g., POST /SOGo/?x= HTTP/1.1 with body x=).
• Logs: Repeated SOGo process crashes or restarts in system logs (e.g., journalctl, /var/log/syslog); segfault entries referencing NGHashMap or sope-core in crash logs or core dumps.
• Process: Unexpected termination of the sogod process; high restart frequency of the SOGo daemon as monitored by process supervisors (e.g., systemd, supervisord) (oss-security).

The fix was merged into the upstream SOPE repository on August 4, 2025 (PR #69), correcting the last pointer maintenance across all NGHashMap methods. Debian issued DSA-5970-1 for bookworm (stable) and DLA-4260-1 for Debian 11 LTS, providing patched SOPE packages. Users should upgrade to a patched SOPE/SOGo package provided by their distribution (e.g., Debian package 5.12.1-2 for trixie, or the DSA-5970-1 update for bookworm). No configuration-based workaround is available; upgrading is the only remediation (GitHub PR #69, oss-security).

The vulnerability was responsibly disclosed by Stefan Bühler on the oss-security mailing list on July 2, 2025, with a patch submitted simultaneously to the upstream GitHub repository. Community commentary on the PR noted the project's slow response to security issues, with the fix taking over a month to be merged (merged August 4, 2025). Debian maintainers proactively included the patch in their packages ahead of the upstream merge. The CISA vulnerability bulletin for the week of June 30, 2025 included this CVE (oss-security, GitHub PR #69, CISA Bulletin).