# CVE-2026-63075: QUIC ACK-only Packet Retention Can Cause Memory Exhaustion

> A remote attacker can cause memory exhaustion and denial of service in OpenSSL by exploiting unbounded retention of ACK-only packet metadata in the QUIC stack.

- **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-2026-63075, AZL-97938, BELL-CVE-2026-63075, CLEANSTART-2026-ZQ04316, DEBIAN-CVE-2026-63075, GHSA-cj75-r57j-r5v8, MINI-7862-q8r2-rq2g, UBUNTU-CVE-2026-63075

## What is CVE-2026-63075?

CVE-2026-63075 is a high-severity denial of service 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: When OpenSSL processes QUIC traffic from a peer that repeatedly
sends ack-eliciting packets while not acknowledging ACK-only responses, the
QUIC stack can retain ACK-only packet metadata for the lifetime of the
connection.

Impact summary: A remote peer that can complete a QUIC handshake can
cause connection-scoped memory growth which may lead to Denial of Service
through memory exhaustion, especially with sustained traffic or many concurrent
QUIC connections.

CWE: CWE-770: Allocation of Resources Without Limits or Throttling

Description: When the OpenSSL QUIC stack sends an ACK-only packet,
there is no requirement by the QUIC protocol that the peer will acknowledge
that ACK-only packet (i.e. it is itself not ack-eliciting). However, the OpenSSL
implementation stores the metadata about the ACK frames regardless.
In and of itself that's ok, but if a malicious peer establishes a connection, and
then drives the connection such that ACK-only packets are forced from the 
OpenSSL implementation peer (i.e., by sending numerous PING frames),
and then withholding any subsequent acks for ack-eliciting data, like
legitimate data, said malicious peer can force inappropriate memory growth
on the OpenSSL peer, potentially leading to a Denial of Service.

The fix is to ensure that we account for the transmission of the ACK-only
packet in the packet histories high and low watermark without actually storing
the ACK-only packet metadata itself.

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

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-63075?

It affects 1 product.


Products: Openssl Openssl.

## How do I fix CVE-2026-63075?

Apply the vendor's patch.

## Is CVE-2026-63075 being exploited?

There is no known exploitation of CVE-2026-63075 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-2026-63075 and fix it if it is affected.

What it is: CVE-2026-63075 is a high-severity denial of service 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-2026-63075 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-2026-63075/ (Markdown: https://insights.sbomify.com/CVE-2026-63075/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63075
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63075
- OSV: https://osv.dev/vulnerability/CVE-2026-63075

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63075/
Summaries are generated and may contain mistakes; the official description above is the record.