CVE-2026-28389: OpenSSL NULL pointer dereference in CMS EnvelopedData processing

CVE-2026-28389 · Severity: high · CVSS 7.5 · Published 2026-04-07

OpenSSL is a widely used security library that provides encrypted communications for websites and applications. A vulnerability in how it handles certain encrypted messages (CMS EnvelopedData) allows an attacker to crash the application by sending a specially crafted message. This results in a denial-of-service, potentially taking down critical services like secure email (S/MIME) or other encrypted communication channels before they can even verify the sender's identity.

Technologies: OpenSSL, Siemens SIMATIC CN 4100, Siemens SIMATIC S7-1500 TM MFP. Vendors: OpenSSL, Siemens.

Quick answers

Is CVE-2026-28389 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-28389 being exploited in the wild.
How severe is CVE-2026-28389?
High severity, with a CVSS score of 7.5, published 7 April 2026.
Which products and versions are affected?
OpenSSL 3.6.0 < 3.6.2, 3.5.0 < 3.5.6, 3.4.0 < 3.4.5, 3.3.0 < 3.3.7, 3.0.0 < 3.0.20, 1.1.1 < 1.1.1zg, 1.0.2 < 1.0.2zp; Siemens SIMATIC CN 4100 < V5.0.
Is there a fix for CVE-2026-28389?
A patch was published on 2026-04-06: Fixes committed to OpenSSL repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-28389 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-28389?
Check whether you run OpenSSL, Siemens SIMATIC CN 4100 or Siemens SIMATIC S7-1500 TM MFP at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A NULL pointer dereference exists in OpenSSL's CMS (Cryptographic Message Syntax) implementation, specifically within the [ec]dh_cms_set_shared_info functions in crypto/cms/cms_dh.c and crypto/cms/cms_ec.c. When processing a CMS EnvelopedData message using KeyAgreeRecipientInfo, the code fails to verify the presence of the optional parameters field in the KeyEncryptionAlgorithmIdentifier before attempting to access it. An unauthenticated remote attacker can exploit this by sending a crafted CMS message that omits this field, causing a SIGSEGV and subsequent denial-of-service. The vulnerability affects applications calling CMS_decrypt() on untrusted input, such as S/MIME mail servers. Patches are available in OpenSSL versions 3.6.2, 3.5.6, 3.4.5, 3.3.7, and 3.0.20.

Affected products

  • OpenSSL OpenSSL 3.6.0 < 3.6.2, 3.5.0 < 3.5.6, 3.4.0 < 3.4.5, 3.3.0 < 3.3.7, 3.0.0 < 3.0.20, 1.1.1 < 1.1.1zg, 1.0.2 < 1.0.2zp
  • Siemens SIMATIC CN 4100 < V5.0
  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem

Timeline

  • 2026-04-06: patched: Fixes committed to OpenSSL repository
  • 2026-04-07: advisory: OpenSSL Security Advisory published

References

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