Answer in brief
CVE-2026-28388 records a High severity (CVSS 7.5) vulnerability in NULL Pointer Dereference When Processing a Delta CRL. The current sources do not mark it as known exploited. The current feed maps OpenSSL/OpenSSL (generic), Siemens/SIMATIC CN 4100 (generic), Siemens/SIMATIC S7-1500 TM MFP - GNU/Linux subsystem (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps OpenSSL/OpenSSL (generic), Siemens/SIMATIC CN 4100 (generic), Siemens/SIMATIC S7-1500 TM MFP - GNU/Linux subsystem (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| OpenSSL/OpenSSLgeneric | >=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 | 3.6.2, 3.5.6, 3.4.5, 3.3.7, 3.0.20, 1.1.1zg, 1.0.2zp |
| Siemens/SIMATIC CN 4100generic | >=0 <V5.0 | V5.0 |
| Siemens/SIMATIC S7-1500 TM MFP - GNU/Linux subsystemgeneric | >=0 <* | * |
Published upstream
Apr 7, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Oct 15, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Oct 15, 2026
Issue summary: When a delta CRL that contains a Delta CRL Indicator extension is processed a NULL pointer dereference might happen if the required CRL Number extension is missing. Impact summary: A NULL pointer dereference can trigger a crash which leads to a Denial of Service for an application. When CRL processing and delta CRL processing is enabled during X.509 certificate verification, the delta CRL processing does not check whether the CRL Number extension is NULL before dereferencing it. When a malformed delta CRL file is being processed, this parameter can be NULL, causing a NULL pointer dereference. Exploiting this issue requires the X509_V_FLAG_USE_DELTAS flag to be enabled in the verification context, the certificate being verified to contain a freshestCRL extension or the base CRL to have the EXFLAG_FRESHEST flag set, and an attacker to provide a malformed CRL to an application that processes it. The vulnerability is limited to Denial of Service and cannot be escalated to achieve code execution or memory disclosure. For that reason the issue was assessed as Low severity according to our Security Policy. The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.
Quoted source text, attributed separately from HOL analysis.