---
id: CVE-2026-28388
title: |-
  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…
summary: |-
  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…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-476
vendor: openssl
product: openssl
affected:
  - 'openssl >= 1.0.2, < 1.0.2zp'
  - 'openssl >= 1.1.1, < 1.1.1zg'
  - 'openssl >= 3.0.0, < 3.0.20'
  - 'openssl >= 3.3.0, < 3.3.7'
  - 'openssl >= 3.4.0, < 3.4.5'
  - 'openssl >= 3.5.0, < 3.5.6'
  - 'openssl >= 3.6.0, < 3.6.2'
patched:
  - openssl 3.6.2
published: '2026-04-07'
updated: '2026-07-24'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-28388'
references:
  - url: >-
      https://github.com/openssl/openssl/commit/59c3b3158553ab53275bbbccca5cb305d591cf2e
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/5a0b4930779cd2408880979db765db919da55139
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/602542f2c0c2d5edb47128f93eac10b62aeeefb3
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/a9d187dd1000130100fa7ab915f8513532cb3bb8
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/d3a901e8d9f021f3e67d6cfbc12e768129862726
    label: openssl-security@openssl.org
  - url: 'https://openssl-library.org/news/secadv/20260407.txt'
    label: openssl-security@openssl.org
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-032379.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-265688.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00885
epssPercentile: 0.59041
ingestedAt: '2026-07-25T23:05:58.130Z'
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-04-10T20:18:04.195701Z'
---

## Overview

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.

## Affected

- `openssl >= 1.0.2, < 1.0.2zp`
- `openssl >= 1.1.1, < 1.1.1zg`
- `openssl >= 3.0.0, < 3.0.20`
- `openssl >= 3.3.0, < 3.3.7`
- `openssl >= 3.4.0, < 3.4.5`
- `openssl >= 3.5.0, < 3.5.6`
- `openssl >= 3.6.0, < 3.6.2`

## Remediation

Upgrade past the affected range:

- `openssl 3.6.2`