# CVE-2026-28388: NULL Pointer Dereference When Processing a Delta CRL

> Attackers can cause a denial of service in applications using OpenSSL by providing a malformed delta CRL when specific verification flags are enabled.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Apr 2026
- **Updated:** 15 Oct 2026
- **Also known as:** ALPINE-CVE-2026-28388, AZL-81953, AZL-82100, BELL-CVE-2026-28388, CLSA-2026-1778020035, CLSA-2026-1778020314, CLSA-2026-1778061272, CLSA-2026-1788860468, DEBIAN-CVE-2026-28388, ECHO-4471-00bd-faf3, GHSA-rpg5-467j-c25q, JLSEC-2026-273, MINI-5h2x-j7mm-7g2q, MINI-jf68-c428-p2q8, MINI-xcv8-qq8r-3pmm, OESA-2026-2078, OESA-2026-2079, OESA-2026-2080, OESA-2026-2081, OESA-2026-2082, ROOT-OS-ALPINE-315-CVE-2026-28388, ROOT-OS-ALPINE-317-CVE-2026-28388, UBUNTU-CVE-2026-28388

## What is CVE-2026-28388?

CVE-2026-28388 is a high-severity vulnerability in Openssl Openssl, published on 7 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-28388?

It affects 1 product.


Products: Openssl Openssl.

## How do I fix CVE-2026-28388?

Apply the vendor's patch.

## Is CVE-2026-28388 being exploited?

There is no known exploitation of CVE-2026-28388 in the wild and no public exploit code.

## Other vulnerabilities in Openssl Openssl

- [CVE-2009-3245](https://insights.sbomify.com/CVE-2009-3245/): Null dereference in n/a (critical 10.0)
- [CVE-2006-3738](https://insights.sbomify.com/CVE-2006-3738/): Memory corruption in n/a (critical 10.0)
- [CVE-2026-63073](https://insights.sbomify.com/CVE-2026-63073/): Untrusted Sender DN Used as Format String in CMP Response Validation (critical 9.8)
- [CVE-2016-6309](https://insights.sbomify.com/CVE-2016-6309/): Use after free in n/a (critical 9.8)
- [CVE-2016-0799](https://insights.sbomify.com/CVE-2016-0799/): Integer overflow in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-28388 and fix it if it is affected.

What it is: CVE-2026-28388 is a high-severity vulnerability in Openssl Openssl, published on 7 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-28388 in the wild and no public exploit code.

Affected product: Openssl Openssl. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-28388/ (Markdown: https://insights.sbomify.com/CVE-2026-28388/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-28388
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-28388
- OSV: https://osv.dev/vulnerability/CVE-2026-28388

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-28388/
Summaries are generated and may contain mistakes; the official description above is the record.