Is CVE-2026-28388 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-28388 being exploited in the wild.

How severe is CVE-2026-28388?

High severity, with a CVSS score of 7.5, published 7 April 2026.

Which products and versions are affected?

OpenSSL 3.6.0 to 3.6.1, 3.5.x, 3.4.x, 3.3.x, 3.0.x; Siemens SIMATIC CN 4100 before V5.0; Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem all versions.

Is there a fix for CVE-2026-28388?

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-2026-28388 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-28388?

Check whether you run OpenSSL, Siemens SIMATIC CN 4100 or Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem 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.

CVE-2026-28388: OpenSSL NULL pointer dereference in delta CRL processing

CVE-2026-28388 · Severity: high · CVSS 7.5 · Published 2026-04-07

OpenSSL is a widely used security library that handles encrypted communications and digital certificates. A flaw in how it processes specific certificate revocation lists (CRLs) could allow an attacker to crash an application by providing a specially crafted file. This results in a denial-of-service, potentially disrupting secure connections or services that rely on certificate verification.

Technologies: OpenSSL, Siemens SIMATIC CN 4100, Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem. Vendors: OpenSSL, Siemens.

Quick answers

Is CVE-2026-28388 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-28388 being exploited in the wild.
How severe is CVE-2026-28388?: High severity, with a CVSS score of 7.5, published 7 April 2026.
Which products and versions are affected?: OpenSSL 3.6.0 to 3.6.1, 3.5.x, 3.4.x, 3.3.x, 3.0.x; Siemens SIMATIC CN 4100 before V5.0; Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem all versions.
Is there a fix for CVE-2026-28388?: 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-2026-28388 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-28388?: Check whether you run OpenSSL, Siemens SIMATIC CN 4100 or Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem 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 X.509 certificate verification logic, specifically within the check_delta_base function in crypto/x509/x509_vfy.c. When delta CRL processing is enabled, the code fails to verify if the CRL Number extension is present before dereferencing it. An attacker can trigger this by providing a malformed delta CRL that lacks the required CRL Number extension. Exploitation requires the X509_V_FLAG_USE_DELTAS flag to be enabled and the certificate or base CRL to indicate the use of delta CRLs. The vulnerability results in an application crash (Denial of Service) but does not allow for code execution or data leakage. Patches have been released for OpenSSL versions 3.0 through 3.6.

Affected products

OpenSSL OpenSSL 3.6.0 to 3.6.1, 3.5.x, 3.4.x, 3.3.x, 3.0.x
Siemens SIMATIC CN 4100 before V5.0
Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem all versions

Timeline

2026-04-06: patched: Fixes committed to OpenSSL repository
2026-04-07: advisory: OpenSSL Security Advisory published
2026-04-07: disclosed: CVE-2026-28388 published

References

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