# OpenSSL Buffer Overflow Puts Siemens Desigo CC Building Systems at Critical Risk
## The Threat
A critical stack-based buffer overflow in OpenSSL's CMS message parsing has landed squarely in Siemens Desigo CC — the building management platform that controls HVAC, access control, fire safety, and energy systems across hospitals, data centers, and industrial facilities worldwide. The vulnerability, CVE-2025-15467, scores a perfect 9.8 on the CVSS scale and requires no authentication, no user interaction, and no special conditions to trigger.
The flaw lives in how OpenSSL processes CMS AuthEnvelopedData structures that use AEAD ciphers like AES-GCM. When parsing the ASN.1-encoded initialization vector (IV) embedded in such a message, OpenSSL copies it into a fixed-size stack buffer without first checking that the IV fits. An attacker sends a crafted CMS message with an oversized IV — the IV gets written past the buffer boundary before any cryptographic authentication or tag verification occurs. The authentication check never runs. There's no key material required to trigger the crash or the write primitive.
That last detail is what makes this particularly ugly: the pre-authentication nature of the overflow means anyone who can reach a Desigo CC service that processes untrusted CMS or PKCS#7 content — S/MIME, encrypted payloads, certificate messages — can trigger it without possessing any legitimate credentials. Actual exploitation to remote code execution depends on platform mitigations like ASLR and stack canaries, but the write primitive is real, the CVSS vector is network-accessible with low complexity, and building automation systems are not renowned for defense-in-depth at the network layer.
## Severity and Impact
| CVE | CVSS Score | Severity | Vector String | Attack Complexity | Authentication | CWE |
|-----|-----------|----------|--------------|-------------------|----------------|-----|
| CVE-2025-15467 | 9.8 | CRITICAL | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H | Low | None required | CWE-787 (Out-of-bounds Write) |
The impact triad — Confidentiality, Integrity, Availability all scored High — reflects the full range of outcomes: from a denial of service crash that takes a building management system offline, to potential code execution that could give an attacker control over the platform managing physical security and environmental systems.
## Affected Products
Siemens Desigo CC — All Vulnerable Versions:
Underlying OpenSSL Versions Affected:
Not affected:
## Mitigations
Apply vendor patches immediately where available:
Compensating controls for unpatched systems:
Siemens recommends validating any security update in a test environment before applying it to production and having trained staff supervise the update process. Automated patching tooling is supported for multi-instance deployments where the product permits it.
## References
---
## HackWire Analysis
The security community tends to focus on OpenSSL vulnerabilities in the context of web servers and enterprise TLS stacks — which makes sense, given how ubiquitous it is. But CVE-2025-15467 hitting Siemens Desigo CC is a reminder that OpenSSL is embedded everywhere, including in operational technology environments where patching windows are measured in months or years, not hours.
Desigo CC is not a web server. It's the platform that tells a hospital's HVAC to maintain negative pressure in an isolation room, that manages access doors in a data center, that controls fire suppression timing in an industrial facility. Taking it offline with a DoS is bad. Getting code execution on it is potentially catastrophic — and the attack surface here is any service that processes external CMS or PKCS#7 messages, which in a building management context often means encrypted communications with field controllers, certificate-based authentication flows, or S/MIME-wrapped alerts.
The pre-authentication trigger is the detail that demands immediate attention from defenders. You cannot filter this at the application layer by requiring valid credentials, because the crash happens before the authentication check runs. Network segmentation is the only reliable compensating control for V7 systems that have no patch path — and that segmentation needs to be tight, not "on a different VLAN."
The broader pattern here is worth naming: critical infrastructure vendors are increasingly shipping products built on the same open-source cryptographic stacks as enterprise software, but without the same patch velocity. When OpenSSL discloses a critical CVE, a web hosting company pushes a fix in days. An OT vendor's patch lands months later, if at all for legacy versions. For V7 Desigo CC operators, there is no patch. That gap is the threat.
— HackWire Editorial
---
## Related Coverage