Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-28388 is a high-severity NULL Pointer Dereference (CWE-476) vulnerability in Openssl Openssl. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique OS Credential Dumping (T1003); ranked in the top 42% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-28388 is a NULL pointer dereference vulnerability in the OpenSSL cryptographic library during X.509 certificate verification. It occurs when processing a delta Certificate Revocation List (CRL) that includes a Delta CRL Indicator extension but lacks the required CRL Number extension. The issue arises specifically when CRL processing and delta CRL processing are enabled via the X509_V_FLAG_USE_DELTAS flag in the verification context, combined with a freshestCRL extension in the certificate or the EXFLAG_FRESHEST flag set on the base CRL.
An attacker can exploit this vulnerability by supplying a malformed delta CRL to a vulnerable OpenSSL-based application that performs certificate verification under the specified conditions. Exploitation is network-based with low complexity, requiring no privileges or user interaction (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Successful exploitation triggers a crash, resulting in a denial-of-service condition for the application, but cannot lead to code execution or memory disclosure.
Mitigation involves applying patches from OpenSSL, available in the following GitHub commits: 59c3b3158553ab53275bbbccca5cb305d591cf2e, 5a0b4930779cd2408880979db765db919da55139, 602542f2c0c2d5edb47128f93eac10b62aeeefb3, a9d187dd1000130100fa7ab915f8513532cb3bb8, and d3a901e8d9f021f3e67d6cfbc12e768129862726. The FIPS modules in OpenSSL versions 3.6, 3.5, 3.4, 3.3, and 3.0 are unaffected, as the vulnerable code lies outside the FIPS module boundary. The issue is rated low severity per OpenSSL's Security Policy despite the CVSS score of 7.5 (CWE-476).
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-19962
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation (including static analysis) directly finds null-dereference bugs before deployment.
Documented development standards and tools can enforce null-safety rules and safe pointer usage.
Engineering principles can mandate defensive coding such as explicit null checks before dereference.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices (static analysis, code review, safe coding standards) directly prevent NULL dereference bugs during development.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.