# CVE-2026-18798: QUIC Server May Trigger Double Free When Processing INITIAL Packet

> A double free vulnerability in the OpenSSL QUIC server allows remote attackers to cause a denial of service via malformed INITIAL packets.

- **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:** 25 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** ALPINE-CVE-2026-18798, BELL-CVE-2026-18798, CLEANSTART-2026-QD52056, DEBIAN-CVE-2026-18798, GHSA-3j55-qf57-hqc2, MINI-mc66-p6g2-353j, UBUNTU-CVE-2026-18798

## What is CVE-2026-18798?

CVE-2026-18798 is a high-severity memory corruption vulnerability in Openssl Openssl, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Issue summary: QUIC server may double free QRX (QUIC record layer RX) object
when channel creation fails for initial packet.

Impact summary: Double free leads to heap corruption, which typically results in 
termination of QUIC server process, leading to Denial of Service. There is so
far no evidence that this double free is exploitable for remote code execution,
thus it is considered highly improbable.

CWE: CWE-415: Double Free

Description: In order to validate initial packet, OpenSSL QUIC stack default
packet handler (port_default_packet_handler()) creates a so-called QRX object.
If the initial packet validates successfully with QRX object, the default packet
handler proceeds to channel (connection object) creation. The QRX object used
for packet validation is passed to port_bind_channel(), so it becomes part of
the newly created connection. If port_bind_channel() fails, then it also frees
the QRX object. Once port_bind_channel() returns, the port_default_packet_handler()
detects the failure and proceeds to the error branch, where the same QRX object is
freed for the second time.

The failure in port_bind_channel() function can be induced with a relatively
low effort by a malformed (non RFC 9000 compliant) INITIAL packet. If the packet
carries DCID (destination connection ID) which is shorter than 8 bytes, then
port_bind_channel() jumps to the error path after ossl_quic_lcidm_enrol_odcid()
detects that the DCID has invalid length.

FIPS impact: no
The FIPS module is not affected, as the QUIC implementation is outside of
the OpenSSL FIPS module boundary.

Weakness: CWE-415 (Double Free)

## Which versions are affected by CVE-2026-18798?

It affects 1 product.


Products: Openssl Openssl.

## How do I fix CVE-2026-18798?

Apply the vendor's patch.

## Is CVE-2026-18798 being exploited?

There is no known exploitation of CVE-2026-18798 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-2026-18798 and fix it if it is affected.

What it is: CVE-2026-18798 is a high-severity memory corruption vulnerability in Openssl Openssl, published on 25 Aug 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-2026-18798 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-2026-18798/ (Markdown: https://insights.sbomify.com/CVE-2026-18798/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18798
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18798
- OSV: https://osv.dev/vulnerability/CVE-2026-18798

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18798/
Summaries are generated and may contain mistakes; the official description above is the record.