CVE-2026-28388
Description
A flaw was found in OpenSSL. When processing a malformed delta Certificate Revocation List (CRL) that lacks a required CRL Number extension, a NULL pointer dereference can occur. This vulnerability can be exploited by a remote attacker who provides a specially crafted delta CRL to an application that has delta CRL processing enabled, leading to a Denial of Service (DoS) for the application.
Statement
Low impact. This vulnerability in X.509 certificate verification can lead to a Denial of Service (DoS) due to a NULL pointer dereference when processing a malformed delta Certificate Revocation List (CRL). Exploitation requires the X509_V_FLAG_USE_DELTAS flag to be enabled in the verification context, a certificate with a freshestCRL extension or a base CRL with EXFLAG_FRESHEST set, and an attacker-provided malformed CRL. This flaw is limited to DoS and does not allow for code execution or memory disclosure.
Mitigation
To mitigate this issue, ensure that delta CRL processing is not enabled in applications that do not require it. This vulnerability is only exploitable when the `X509_V_FLAG_USE_DELTAS` flag is explicitly set within the X.509 verification context. Review application configurations to confirm that this flag is not enabled unless absolutely necessary for your security policy. Disabling this flag will prevent the vulnerable code path from being exercised. Specific implementation details will vary depending on the application utilizing X.509 certificate verification.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 7.5 | 7.5 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | Low | Low |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | None | None | None |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
Integrity,Confidentiality
Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
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